Tornadoes(龙卷风) are one of the worst weather events on earth. Each year, tornadoes kill many people. The storms often carry homes, cars and trees from one place to another. And they can also destroy anything when they pass by.

      A tornado comes from a thunderstorm(雷雨) in the sky down to the ground. It is big at the top and small at the bottom.

      A tornado appears when winds in different directions meet in the cloud and begin to turn in circles. People can see tornadoes almost everywhere in the world. But most happen from late winter to middle summer. There is a second high season in November. During spring, warm air moves north and mixes with the cold air left from winter. In November, the opposite happens. Cold air moves south and mixes with the warm air left from summer.

      Tornadoes always come suddenly. Weather scientists have done something to predict(预测) tornadoes. But the storms often move too fast for people to protect themselves. Last year, tornadoes killed more than one hundred people in United States.

      Scientists say the best place to be in is a small room, without windows, in the middle the lowest part of a building when tornadoes come.

    Personal planes which can take off noiselessly from the back garden will be possible within two years.

    Lilium Aviation is inventing an electric two-seater airplane which  takes just 20 hours to learn to fly and can travel at speeds of  250mph.More importantly, the small plane, which weighs just 25kg, can take off vertically which means it does not need to fly from an airport, but could be parked outside a house or in a garden. The company says the design will “open the door to a new class of simpler, quieter and environmentally friendly planes” and will be possible from 2018.

    “Our goal is to develop an airplane for use in everyday life,” said Daniel, CEO and one of the company's four founders. "We are going for a plane that can take off and land vertically and does not need the difficult and expensive infrastructure of an airport.

    Although helicopters offer a choice, they are very noisy and difficult to fly and require expensive licenses. They also have no backup if the rotor fails, making them costly to build and keep. While firstly limited to airfields, the Lilium airplane will eventually take off vertically from almost anywhere – even from back gardens – it needs only an open flat area of 50 ft. by 50ft (15 m x 15m).

    The plane is classed as a Light Sport Aircraft for two users, with the pilot's license requiring 20 hours' minimum training – almost like taking a driving license. It is intended for fun flying during daylight, in good weather conditions and in least crowded airspace up to 3 km altitude. The airplane would have to follow the same flight laws as helicopters.

    How much sleep do we need? We are all different. Some people need only three hours of sleep a night. Others need ten hours of sleep a night. Most Americans sleep an average(平均) of seven to eight hours a night. After the age of fifty, the average sleeping time goes down to 6.5 hours a night.

    Most people have a bad night when they cannot fall asleep(睡着). The name of this problem is called insomnia.

    This isn't a new problem .Many famous people in history had insomnia .Some of these people had special ideas to make them sleep .Benjamin Franklin, the famous inventor had four beds. He moved from one to another to fall asleep .King Louis XIV(国王路易十四)of France had four hundred and thirteen beds and hoped to fall asleep in one of them .Mark Twain, the famous American writer, had a different way. He lay on his side across the end of his bed.

    Can dolphins (海豚) talk? Maybe they can not talk with words, but they can talk with sounds. They show their feelings with sounds. Dolphins travel in a group. We call a group of fish a "school". They do not study, but they travel together. Dolphins are mammals (哺乳动物), not fish, but they swim together like fish in a school. Dolphins talk to the other dolphins in the school. They give information to the others. They talk when they are happy, sad or afraid. They say "welcome" when a dolphin comes back to the school. They talk when they play.

    They make some sounds above water. They make many more sounds under water. People cannot hear these sounds because they are very, very high. Scientists make tapes of the sounds and study them. Sometimes people catch dolphins for a large aquarium (水族宫). People can watch dolphins in a show. Dolphins do not like to be away from their school in an aquarium. They are sad and lonely. There are many stories about dolphins. They help people. Sometimes they save somebody's life. Dolphins' meat is good, but people do not like to kill them. They say that dolphins bring good luck. Many people believe this.

    When we think of paper, we think of newspapers and books. But there are many other uses. Only half of the world's paper is used for books and newspapers.

    Paper is very good for keeping you warm. You have perhaps seen homeless men sleep on a large number of newspapers. In Finland, it is sometimes-40℃ in winter. The farmers wear paper boots(靴子)in the snow. Nothing could be warmer.

    Each year, more and more things are made of paper. We have had paper cups and plates for a long time. But now we hear that chairs, tables, and even beds can be made of paper. Besides paper boots and shoes, you can wear paper hats, paper dresses, and paper raincoats. When you have used them once, you may throw them away and buy new ones.

    The latest use of paper seems to be paper houses. These are not small houses for children to play in, but real, big houses for people to live in. You can buy a house with three rooms for about 500 dollars. You can put it up by yourself in a few hours, and you can use it for about five years.