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.

阅读下面短文，从A、B、C、D四个选项中选出最佳选项。

    Almost everybody in America will spend a part of his or her life behind a shopping cart. They will, in a lifetime, push the shopping carts many miles, but few will know—or even think to ask—who it was that invented them.

    Sylvan N. Goldman invented the shopping cart in 1937. At that time he was in the supermarket business. Every day he would see shoppers lugging groceries around in baskets they had to carry.

    One day Goldman suddenly had the idea of putting baskets on wheels. To create the first shopping cart, Goldman used folding chairs. He out one basket on the seat, and he raised the chair by putting wheels under the legs. The wheeled baskets would make shopping much easier for his customers, and would help to attract more business.

On June 4, 1937, Goldman's first carts were ready for use in his market. He was terribly excited on the morning of that day as customers began arriving. He couldn't wait to see them using his invention. However, Goldman was disappointed. Most shoppers gave the carts a long look, but hardly anybody would give them a try. After a while, Goldman decided to ask customers why they weren't using his carts.

    "Don't you think this arm is strong enough to carry a shopping basket?" one shopper replied.

    Goldman wasn't beaten yet. He knew his carts would be a great success if only he could persuade people to give them a try. To this end, Goldman hired a group of people to push carts around his market and pretend they were shopping! Seeing this, the real customers gradually began copying the phony customers.

As Goldman had hoped, the carts were soon attracting larger and larger numbers of customers to his market. Not only did more people come—those who came bought more. With larger, easier-to-handle baskets, customers unconsciously bought a greater number of items than before.

    Today's shopping carts are five times larger than Goldman's original model. Perhaps that's one reason Americans today spend more than five times as much money on food each year as they did before 1937—before the coming of the shopping cart.

    It is park at the bottom of the ocean. It's cold down there too. There's no air to breathe. The water pressure is high. There may be fishes that could hurt you. The deep sea can be an unpleasant place. But people are still fascinated by it, not just because of the amazing scenery. The seafloor might hold the secret to the beginning of life on Earth.

    Oceans cover more than two-thirds of our planet. Yet, we have explored just a small part of the underwater world. A new project is there to explore the ocean deeper. A new US machine can carry people down to as deep as 6,500 metres. It will take the place of an older machine called Alvin. The old one has been in use for 40 years, but it can only go down to 4,500 metres. Alvin played a key role in many important tasks. Alvin helped biologists collect worms, chemists gather rocks, and oceanographers (海洋学家) map the seafloor and take water sample (样本).

    But now it's about time for a new one. The new machine will be like Alvin. It'll also be about 27 feet long, about the size of a small school bus. The seating area inside will be small, about two metres wide. Like Alvin, it'll carry a pilot and two passengers. It will be able to move like Alvin does. It'll give passengers more chances to enjoy the view. Alvin has only three windows. The new one will have five. It will travel more than a mile an hour faster than Alvin. Getting to the bottom faster and moving around more quickly will allow researchers to make the most of their time underwater.

    One morning while Officer Vogel was on his coffee break in a restaurant, a man ran in a yelled. "Officer! A little kid is driving a car down the street!"

    He ran out at once and saw a car going slowly--about 25 miles an hour--but it was going very straight. He jumped into his police car and followed it. When the car was stopped, Officer Vogel looked inside. The driver was a little boy. His name was Rocco Morabiro and was 5. In the back seat was his two-year-old sister. Both children wen crying.

    "I want my mummy!" the boy cried." But she can't get here. I have the car." Then he had an idea." Just a minute." He told Officer Vogel." I can drive. I'll go to get her."

    "No!" Officer Vogel said. "You stay with me!" Then he drove them to the police station and he called their mother. They had many questions for Rocco. The first question was: "Where did you get the car keys?"

    Rocco said. "From the top of the refrigerator." At seven that morning Rocoo's father was work and his mother was sleeping, Rocco saw the keys on top of the refrigerator. He climbed on a chair, and took the keys.

Rocco got into the car and started the engine (引擎). When Rocco's sister heard the engine she ran to the car and cried. She wanted to go with him.

It was 7 a. m.—rush hour—so there was much traffic. Rocco drove one mile in heavy traffic. Then Officer Vogel stopped him.

    Newspapers and TV stations heard about Rocco, and a lot of reporters went to his house. Areporter asked Rocco, "What do you want to be when you grow up?"

    "A truck driver," he said, smiling.

    RIVER DOLPHIN RUNNING OUT OF TIME

The Yangtze dolphin is the only kind of dolphin that lives in freshwater all its life. Scientists say that the finless freshwater dolphin that has lived in the Yangtze River for over 20 million years, will die out in 15 years. It's in danger of disappearing forever.

    Dangers:

    Dredging(挖掘) of their habitat

    Heavy boat traffic in the Yangtze River

    Insecticide(杀虫剂) and mercury(汞)