How does a periscope work?

A simple periscope can be done using two flat mirrors, inclined at 45 °. The light is reflected by the mirror from the top to the bottom. It is then possible to see an object over a wall, or over the water, when one is in a submarine.

The submarines have periscopes that allow you to see what's going on over the water when the device is submerged. Sometimes submarines sail by letting their periscope pass. But the longest of the periscopes, 27 m, is on land, in a laboratory in the United States where you can study nuclear reactors without exposing yourself to dangerous radiation.

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How do some fish produce electricity?

                         


About 250 kinds of fish can produce electric shock. This allows them to head into muddy waters and also kill their prey. The most powerful electric fish can emit shocks of several hundred volts, enough to stun a human. They have special muscles that act like batteries.
Some name of the fish that produces electricity:
Electric eel, Peters' elephantnose fish, Malapterurus electricus...

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What about cotopaxi?

From time to time it erupts because it is one of the largest active volcanoes in the world.
For 400 years it has erupted 50 times, the last eruption lasted from August 2015 to January 2016. Top of 5897 m, it is located in Ecuador.

Also:

Mauna Loa is the largest volcano in the world. It is on the Hawaiian Islands measuring 119 km at its base.

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What is a glacier?

A glacier is a moving ice field. It is found in the polar regions and in the high mantains, everywhere there is more snow in winter than it can melt and evaporate during the summer. The smooth mass slides slowly down the slopes, modeling the landscape and sculpting the valleys. If a glacier reaches the sea in a very cold area, huge blocks of ice blocks break up and form icebergs. The largest in the world are in Antarctica.

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What is an amphibian?

                         What is an amphibian?

It is sort of the intermediate step between fish and reptiles. Most spend the first part of their lives in water and their adult phase on earth. They have moist skin and lay their eggs in water or in a very humid environment. They live near water, especially in swamps, but can not survive in the sea
Amphibians are found all over the world, except in very hot regions.

Most of them have four legs, except for the Cecilies, who have none at all.

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Where is the Carpathian Mountains?

These mountains are located in central Europe. They follow the border between Slovakia and Poland and extend as far as Romania. Lower than the Alps; their highest peak only reaches 2655 m. They also have fewer lakes, waterfalls and glaciers.

Also:

• After Russia, the largest country in Europe is Ukraine. France is third.
• Europe owes its name to Europe, a princess of Greek myths. 

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Where was the kingdom of Benin?

The kingdom of Benin was in West Africa, south of the Niger River. 400 years ago, his people made beautiful objects in ivory, wood and bronze. By the year 1000, powerful African kingdoms such as Benin, Kanem-Bornou and Songhaii reigned over West Africa.

Also:

• Africa exports oil, diamonds, gold, and other minerals such as cobalt.
• South Africa produces most of the world's gold.
• Africa's crops include maize, cocoa, tea, cassava, ingame, coffee, sugar, vanilla, bananas and rubber.
• The crops of Africa are: maize, cocoa, tea, cassava, yam, coffee, sugar, vanilla, bananas and rubber.
• about a quarter of the world's forests are in Africa.
• about 40% of Africa's manufactured goods come from South Africa.

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What are the Everglades?

The Everglades are subtropical marshes in south Florida, southeast of the United States. Their area exceeds 7000 km². In places the cutting grass is sometimes 4 m high. Elsewhere, there are salt marshes and mangroves. Before the seminole Indians took refuge there around 1840, no one lived in this region. Partly drained for use in agriculture, the region is now a national park where you can see turtles, alligators and many species of birds.

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How does a volcano erupt?

During an eruption, magma (molten rocks) from the depths of the earth rises to the surface.
Lava (name given to the magma that is pushed outside), red and burning, flows from the volcano.
Smoke and ashes are spewed to the sky and darken.
An active volcano contains thick lava, which rises very slowly and can form a closing pellet. The pressure increases until the gases and ashes pierce it and blow it up, causing a huge explosion.

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The Komodo dragon

 Unlike the fabulous winged monsters of legends, the Komodo   dragon does not spit fire, nor does it fly.
 This massive animal with a big head and a long thick tail is the   largest of the current lizards. 
He lives on a few islands in Indonesia  and feeds on deer and wild   pigs. The Komodo Dragon was discovered by Western scientists in 1910.

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Bonsaï

                                                                  bonsaï

  

• It is a tree that grows in pot like a plant and is grown to be the reduced model of a tree. 

      (Native to Japan)

                                  

      Bonsai are planted in narrow pots and rationed (food). 
The roots and shoots are pruned when the tree grows. The branches are twisted and tied by threads so that the adult tree does not exceed 50 cm.
when mature, the plant looks like an old gnarled tree

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Why should we avoid a phalloides amanita?

Because it's a deadly dangerous fungus. It is best to avoid touching a wild mushroom, unless you know exactly which ones are harmless and which ones are dangerous.

The fly agaric is one of the deadliest mushrooms. His red hat makes it easy to avoid.

Fly agaric is very toxic. Formerly we used his juice to kill flies and bugs.

The word ''amanite '' comes from the Greek amanitès which designates a whole family of mushrooms.

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Which plants have no roots, leaves or flowers?

Lichens, which are an assemblage of algae and mushrooms living together. Some lichens grow in patches on stones and trees.
They grow very slowly and live very old (10,000 years). They are among the oldest living things and survive in places that are too bare, too dry, too cold or too hot for other plants.

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Why does the Puffball explode?

The giant Puffball is a big round mushroom. Its skin is paper-thin, swollen from the inside and explodes when a drop of water touches it, leaving a cloud of spores.
Most mushrooms produce a fruit, which is the part we see, the rest of the mushroom is underground or in wood. Some are edible, but others are poisonous.

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What is giant kelp?

It is the largest of the algae. It can measure up to 60 m long and when several kelp grow together they form an underwater forest. Kelp is an ideal shelter for many fish, lobsters and other marine creatures. There are several kinds of kelp, all are brown algae that live in cold waters.

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What is the difference between a butterfly and a moth?

Moths are often thought of as dull insects, flying at night and having a large, hairy body, and butterflies as brightly colored insects, flying during the day.

But there are many colorful moths that fly during the day.

The six-spotted sphinx and saturnia are examples. The real difference lies in the shape of the antennas and the link between the front and rear wings. 

      

                            Moth                                           

The antennae of a butterfly are long and surmounted by a hump, while those of a moth are fine and downy.

At rest, most butterflies fold their wings, showing their lower motives, while the moths keep their wings spread.

  butterfly

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Which regions did Jacques Piccard explore?

This Swiss scientist plunged, in bathyscaphe, into the deepest part of the Pacific Ocean.
With US Navy officer Don Walsh, he broke a record of descent, reaching 10 910 m deep in the Marianas Trench, the deepest underwater valley.

 Learn more:

• Marco Polo was only 17 when he began the difficult journey from Europe to China.
•  Livingstone was the first European to see Victoria Falls in Africa. 
• In 1863 John Hanning Speke proved that the Nile had its source in Lake Victoria.
•  In 1969, two American astronauts, Neil Armstrong and Edwin Aldrin, set foot on the moon. 
• The brothers Verendrye two Frenchmen, are probably the first Europeans to see the Rockies, around 1740

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Which regions did Lewis and Clark explore?

Two US Army officers, Meriwether Lewis and William Clark, traveled from 1804 to 1806 across North America to draw map. They left St. Louis, went down the Missouri River, and crossed the Rockies. Then they explored the west of the Columbia River to the Pacific, before returning to the east. Lewis and Clark mapped many tracts in the West, showing the way for future travelers from California and other western territories.

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Who was Ned Kelly?

In Australia, in the nineteenth century, the outlaws were known as 'Rangers of the bush'. Ned Kelly was the last and most famous of these men. Born in 1855, he formed a gang with his brother, attacking wealthy landowners and stealing horses. Their exploits made them famous, and some poor farmers regarded Ned Kelly as a kind of Australian Robin Hood. But his gang was one day captured by soldiers in Glenrowan. All the outlaws were killed, except Ned Kelly, who wore special protection that he had made. He was wounded and captured, and executed in 1880.

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Story of Robinson Crusoe

The story of Robinson Crusoe was written by Daniel Defoe, an English journalist, in 1719. This book was very successful and is still popular. Defoe was inspired by real stories, including that of Alexander Selkirk, a Scottish sailor who survived a sinking. In this novel, Defoe describes Robinson's lonely life, wrecked on a deserted island for twenty-eight years

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Phallus impudicus

Phallus impudicus is a fungus that produces an odor that attracts flies. For us it smells bad but flies appreciate.
They feed on the sticky liquid that contains the spores and thus carry them on their paws.
Phallus impudicus can spread over a vast territory, helped by flies.

                                              Phallus impudicus

To know also:
The first terrestrial plants appeared 400 million years ago.
Unlike the water lens (duckweeds) they had tubes to suck the water and rigid rods. But no leaves, no roots, no flowers, unlike today's plants.

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Why do we have to sleep?

No one is sure to have the right explanation. Of course, sleep rests the body, new cells are formed, the tissues are repaired.
But during sleep, the brain is very active. Some think that it sorts the events of the day, classifies the new information and organizes them with those already recorded.
This work can be used to learn from new experiences.
A newborn needs 16 hours of sleep a day, at 65 years 6 hours is enough. The areas of the brain that control movement and language remain awake: we can talk, sit and even walk in sleep, no one knows why we do it, and we do not remember when we wake up.

• We sleep, on average, 8 hours a day,  20 years in a lifetime!
• During sleep the heart rate is slowed down.
• Sleep consists of 4 or 5 cycles, which last from 60 to 100 minutes.
• They start with slow sleep and end with REM sleep.(Rapid Eye Movement)
• In adults, slow sleep accounts for about 80% of total sleep.
• Growth hormone is secreted during slow sleep.
• We dream mostly during REM sleep.
• We sleep more when we are sick because our body needs rest to get better.

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Why do we dream?

We all dream every night, but we forget most of our dreams. According to the psychoanalyst Sigmund Freud, our dreams reflect our desires and fears, but in a disguised form. Some dreams could be the way the brain uses to classify the events of the day.

• Four out of five dreams are in color, but we almost always describe them in black and white.
• Dreams fade from memory. If one wakes up more than 10 minutes after dreaming one remembers nothing.
• The animals also dream: often the dogs shake their legs while sleeping as if they were running.
• A phobic can be paralyzed by his fear.
• Agoraphobia is the fear of the great outdoors.
• Claustrophobia is the fear of closed places.
• The Arachnophobes have the phobia of spiders, although they know they can not hurt them.

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What are the most powerful microscopes?

The best light microscope can not amplify an object more than 200 times its size. 

light microscope

The electron microscope can do it over a million times. Electromagnetic fields play the role of lenses.

electron microscope

 A heated filament sends rays of electrons, while the rest continues its journey to a screen or a photographic plate. We obtain the drop shadow of the object.

To know also:

                           Who invented the microscope?
The microscope was invented in the early seventeenth century and attributed to various inventors, including the Dutch Zacharias Jansen. What is surprising is that the lenses were known and manufactured for 300 years, but until that date nobody had thought to combine them to make either a microscope or a telescope.

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The first photograph

The first was taken by the French Nicéphore Niepce, in 1826. It was made on a tin plate, with a layer of bitumen, and showed a view of a window.
The exhibition lasted eight hours.
around 1830-1840, two photographic processes were developed:
the daguerreotype of French L.J.M.
Daguerre and the calotype of the Englishman W.H.Fox Talbot. The daguerreotype used a silver-plated copper plate, instead of glass, exposed for a minute.
In 1888, the American George Eastman developed the Kodak camera, which exhibited rolls of film instead of plates.
*It was so long to be photographed at the end of the nineteenth century that back support was needed to stay put. If we blinked, they were blurry.

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Lighter than air

                                          The Airship

The air has a density, anything less dense than it can float there-just as a piece of wood, less dense than water, floats. Some gases, such as helium and hydrogen, are less dense than air. A balloon or airship inflated to one of these gases floats in the air. Hydrogen is the least dense of all gases but, extremely flammable, it is also of a dangerous use. Probe balloons and airships are usually inflated with helium, non-flammable. Heated, a gas expands and loses its density. it is therefore possible to build a balloon and inflate it with hot air. Balloons are used for sporting and recreational purposes.

                                    Hot Air Balloon

The first hot-air balloons were designed in 1783 by two Frenchmen, the Montgolfier brothers, who were papermakers, so that the first balloons were made of paper or silk. Nowadays, the balloon is made of synthetic fabrics.
A butane burner, at its base, sends hot gases into the balloon and the passengers settle in a platform suspended under the burner. Modern balloons have reached altitudes above 35 km.

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What is cassava?

Cassava is an essential food plant in many tropical countries. Its roots are used to make flour, bread and tapioca. The roots resemble the tubercle of a dahlia. This plant contains cyanide, which protects it from locusts and other insects. Cassava must be cooked to catch its poison. We also use to make glue.
*Cassava grows in hot regions of Asia and Africa.

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Where is the highest waterfall?

The waterfalls are located in the upper reaches of a river where it crosses a layer of hard rock, the slow erosion of which forms a drop which is gradually accentuated. The water of the river dives over this break of are bed. From Salto Del Angel, in Venezuela, in South America, the water falls on 807 m, in a single fall. It is the highest waterfall in the world. With its other sections, one counts waterfalls on 979 m.

           The Salto Del Angel was discovered in 1935 by an American pilot named Jimmy Angel.

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What is the largest lake in the world?

The Caspian Sea, bordered by Russia, Azerbaijan, Turkmenistan, Kazakhstan and Iran, is the largest enclosed expanse of water in the world. Its surface is approximately 372 000 km² and its length of 1200 km (it would be shrinking). Its waters being salty, it is considered a sea rather than a lake. A canal connects it to the Black Sea.

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The strongest earthquakes

Among the strongest earthquakes are those that occurred in China. In 1556, the Shensi earthquake killed about 800,000 people. Then, in 1976, the story was repeated. The Tangshan earthquake, which claimed about 750,000 lives, was one of the greatest disasters of modern times.

• During the eruption of Krakatoa, in 1883, we heard the explosion in Australia, 5000 km from there.
• In 1995 an earthquake struck Kobe. in Japan. 5000 people were killed and half a city was destroyed.

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Which plant has the biggest flower?

The largest flower belongs to rafflesia, or nauseating parasitic lily, from Southeast Asia. It has a diameter of one meter. This flower smells like rotten meat. Unpleasant for humans, this smell attracts many insects that pollinate the plant. Rafflesia is a parasite that grows on the stems and roots of shrubs.

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What are supernovas?

A supernova is a star that suddenly ignites, becoming millions of times brighter. So brilliant that it can be seen in broad daylight; but very quickly it weakens. It is a rather rare sight, because this explosion marks the end of a big star. The last of our galaxy was seen by Kepler in 1604.

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What is belladonna?

Belladonna is a very poisonous plant. Belladonna means: 
''beautiful lady'' in Italian, it has been given this name because it contains atropine.
If atropine is injected into one eye, the pupil dilates. At one time, women used it to make their eyes look better. Nowadays only doctors use it to facilitate exams.

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Who was Admiral Nelson?

Nelson was a hero of the British Navy. Born in 1753, he joined the Navy at only 12 years old. He lost his right arm and the use of the right eye during a battle. In 1798 he defeated the French fleet at the Battle of the Nile and in 1801 he won another victory in Copenhagen, Denmark. Nelson became an English hero. He was given the title of viscount. In 1805 he led the British fleet to victory against France and Spain at Trafalgar. During this battle, he was wounded on the deck of his boat, the "Victory", and died shortly afterwards.

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How many species of algae are there?

There are 7000 of them, most of whom live near the shore where they can cling to the rocks or the bottom with a special foot. Attached to this foot, the fronds oscillate in the water. 
Most brown algae live in cold waters and some become huge. 
Red algae are more prevalent in warm waters. 
The blue algae live in hot or cold waters * The branches of the seaweed are called fronds. Some have vesicles that help them float.

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Which fruits are exploding?

A plant must disperse its seeds to give them the maximum chance of becoming a new foot. One way to do this is to project them from an explosive capsule or pod. The laburnum and other plants of the pea family have pods. When a laburnum pod dries out, it splits, the two halves twist and scatter the seeds so that each new plant has room to grow.

Ecballium (donkey cucumber) projects its seeds by a jet of water from its fruits.
The internal pressure exerted by the water expels the seeds sudainly.

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Do you know where the black forest is?

In the south of Germany, the Black Forest (Schwarzwald in German) is a mountainous region covered with coniferous forests. The Danube takes its source and the Rhine runs along its edge to the west. With its trees with dark leaves, it is a remnant of the vast forests that once covered most of northern Europe

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Who was Helen of Troy?

The Greeks said she was the most beautiful woman in the world. Helen was the daughter of Zeus, the king of the gods. His beauty provoked the war between Greece and Troy. Helen was kidnapped by Paris, the Prince of Troy. Her husband Menelaus wanted revenge and, with his brother Agamemnon, he raised a Greek army against the Trojans. The war lasted ten years

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Where do lemurs live?

Only on the island of Madagascar. The lemurs are an ancient species, close to the ancestors of the monkeys, but they are less evolved and have disappeared from all the borders of the planet. The monkeys took possession of their territories. The lemurs survived only in Madagascar, because the monkeys never reached the island.

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What is the Parthenon?

The Parthenon is a magnificent Greek temple located at the top of the Acropolis, a hill overlooking Athens. Built in honor of the goddess Athena in the fifth century BC J.-C., On the orders of the politician Pericles, it is one of the most famous buildings of the ancient world

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What is a Tasmanian devil?

This animal is a marsupial, close to kangaroos and koalas. The first Europeans to reach Australia called it "Tasmanian Tiger" because of the bands on its back. The Tasmanian tiger or devil, its real name thylacine, was considered extinct but its presence is sometimes reported in remote areas of Tasmania. They once populated the entire Australian territory

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What event commemorates the Eiffel Tower?

The Eiffel Tower, designed by Gustave Eiffel, was built for the Paris World Fair in 1889. This exhibition commemorated the French Revolution, which began a century earlier.
The Revolution began July 14, 1789 by a riot. The angry population attacked Bastille, a prison in Paris. People destroyed the building stone by stone. The French Holiday of July 14, 1789 celebrates the anniversary of the destruction of the Bastille.

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Why is the giant panda rare?

This animal has probably never been widespread in China.
It depends entirely on bamboo forests to feed itself. Each panda has a very large territory because it needs a huge amount of food.

The forests are being destroyed to make way for agriculture and the habitat of the panda is gradually disappearing.
The remaining bamboo plots are often small and can only house two or three panda that can not join other pandas to breed. These small isolated groups are therefore doomed to disappear. Some pandas live in zoos but attempts to breed in captivity are rarely successful

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Have you heard about the piranhas before?

Their aggressiveness is legendary. They have large triangular teeth sharp as razors planted on a jaw powered by very powerful muscles.

 This allows them to snatch flesh pieces very effectively.
Unlike most carnivorous fish, piranhas hunt in schools. their aggression is linked to the breeding period or the males keep the eggs.

They live in the rivers and streams of South America and are attracted by traces of blood and disturbances in the water.
A reliable source speaks of an agouti, a rodent of 45 kg, reduced to a skeleton in less than a minute.

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What is the mystery of Easter Island?

                    

The easter island is located in the middle of the Pacific, 3540 km west of Chile. His monumental statues have made him famous. Carved with stone axes, these statues are the work of a people who came by boat from South America or Polynesia and who left the island a long time ago. It is thought that the statues were erected after the year 400. We do not know what they were intended for: it is the mystery of this island.

During a war in the 18th century, many of them were broken.

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why do we yawn ?

                                                      why do we yawn ?

yawn seems to be the way the body uses to bring more oxygen to the brains , when we yawn we inhale slowly and deeply, then we will expire, we yawn especially when we are tired or bored. refreshing your face can help stop yawning it is impossible to hold back a yawn and the animals are yawning too

*learn more:

• babies' lungs are pink. it darkens as we get older because the air we breathe is dirty

• In the rest we inhale and exhale about 500 cm³ of air 13 times per minute. 

• the lungs of an adult man have an average capacity of 6 liters
• those of a woman 4.5 liters

• in ancient times people believed that the soul and the breath were the same thing

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what are salamanders and newts?

                                   what are salamanders and newts?  



They are amphibians with a long cylindrical body, a long tail and two pairs of legs.
Salamanders are normally larger and spend less time in the water. They are often confused with lizards, but their rounded heads and smooth skin contrasting with the pointed head and scaly skin of lizards, are a great way to differentiate them

Salamander

 Newt

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The dodo

This bird, unable to fly, lived on Mauritius in the Indian Ocean. 
Dodos were not afraid of humans, so sailors could easily catch them and fill their boats with meat. 

On the islands, there were no big predators to threaten the birds and they did not need to know how to fly. So when sailors landed with cats and rats, the dodos were lost in advance. Survivors who do not fly, like the ostrich, have defenses: powerful legs to escape or to hit the enemy

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Who was Davy Crockett?

                            

   Davy Crockett was born in Tennessee in 1786. In his youth, he spent most of his time in the mountains, hunting bears and fighting the Indians. He later became a politician and was elected to the United States Congress. 

In 1835, defeated in elections, he went to Texas to help the inhabitants of this region in their battle for independence (Texas belonged then to Mexico). 

In 1836, during the famous battle of Fort Alamo against the Mexican army, Davy Crockett was one of the 200 defenders killed                       

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Who reached the North Pole first?

                           Who reached the North Pole first?


American explorers Frederick Cook and Robert Peary both claimed to have been the first to reach the North Pole, Cook in 1908 and Peary a year later. In fact, it is possible that they have turned back the road before having reached the North Pole. The first person who really reached the North Pole was the American explorer Richard Byrd with his co-pilot Floyd Bennett, flew over the North Pole on 9-May-1926 
The first to travel across the ice to the North Pole is Ralph Plaisted, Arrived there on April 19- 1968.

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