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A．To keep her carpet clean.B．To protect her carpet.C．To avoid tripping on the carpet.D
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听力原文： One way that scientists learn about man is by animals, such as mice, rats and monkeys. The scientists in this laboratory are experimenting on mice. They are studying the relationship between diet and health. At this time over one hundred experiments are going on in this laboratory.
In this experiment, the scientists are studying the relationship between the amount of food the mice eat and their health. The mice are in three groups. All three groups are receiving the same healthy diet. But the amount of food that each group is receiving is different. The first group is eating one cup of food each day, the second is eating two cups, and the third group of mice is eating three cups.
After three years, the healthiest group is the one that is only eating one cup of food each day. The mice in this group are thinner than normal mice. But they are more active. Also they are living longer. Mice usually live tot two years. Most of the mice in this group are still alive after three years. The second group of mice is normal weight. They are healthy, too. They are active, but not as active as the thinner mice. But they are only living about two years. The last group of mice spends most of the day eating or sleeping. They are not very active. These mice are living longer than the scientists thought: about a year and a half. But they are not healthy. The experiment is still going on. The scientists hope to finish their studies in two years.
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A．A round piece of stone.B．A heavy log.C．Two slices of log connected at their centers
The author claims that there are many people who often laugh at the idea that there are UFOs.
Flying Objects
It is sometimes reported that strange objects have been seen high up in the air. These Unidentified Flying Objects (UFOs) have caused a lot of interest. Some of the reports about them are difficult to believe. Some have been explained in scientific ways. Others have never been explained.
It is not easy to decide whether a report is true or not. One report of an unidentified object came from a British aeroplane on its way from New York to London in 1954. The British machine was flying over an island at 19,000 feet when the captain and others on board noticed something on the left and rather lower than their aeroplane. It was about five miles away.
"It became clear," the captain said, "that it was not one object but several. We saw one large object and six smaller objects. I sent out a radio report about it, and I received the answer that fighter planes were coming out to meet us. Before the fighters were in sight, the smaller objects entered the big object. The big object then became smaller and moved away fast—unbelievably fast."
The captain later answered a lot of questions from newspapermen.
"How long did you have for studying the objects, Captain Howard？"
"They stayed with us for about six minutes."
"What shape were the objects？".
"The large one was continually changing its shape, but each of tile smaller ones was round like a ball."
"What do you mean by 'changing its shape', Captain？"
"Well—at one time the big one had the shape of a telephone receiver, but sometimes it was round When it flew away it seemed to be rather like a very big plate in shape."
"Tell us, Captain Howard—err—were you afraid？" "I truthfully say that I wasn't. None of the people in the plane felt any fear. We talked about that, and we all agreed that in fact we felt friendly towards the objects."
There are other accounts of flying objects which have been seen from the air or from the ground. And many of those who have told us about them are men like Captain Howard—men of sense and experience, men whose word can be trusted.
Dennis Bardens, who wrote the book Mysterious Worlds, tells us that he once saw a UFO himself. He had dinner one night with a friend near Tripoli, Libya, and after dinner the two men walked across to his room to look at some papers. Bardens noticed a light high up over the sea. It was a red light.
He turned to his friend, and mentioned that the moon looked strange that night.
"It isn't the moon," was the reply.
They watched the light and saw that it was moving. It seemed to be an object rather like a big plate. In some ways it looked like smoke with a light on it; but it was not smoke because it did not change its shape. It was moving in a regular way. That is to say, it did not go suddenly faster or more slowly, and it did not go higher or lower. So the two men decided that there must be men in it.
When it came nearer to Libya, Bardens says that he felt eyes looking at him. He was being watched in the darkness.
When it was nearer, they noticed that the bottom parts were brighter than the top. The bottom was yellow and the top red. Then the object suddenly turned away and left Libya, moving very fast.
On a later day Bardens talked to other people about it, and he found some who had seen it. They all described it in the same way. Could they all be mistaken？
Other people in different parts of the world believe that they have seen UFOs. Those who used to laugh at the idea do not laugh so often now. A lot of reports and books have been written on this subject, and it seems impossible to take no notice of them. Few people really believe it's UFOs, but perhaps they will in the future. Let us consider another of the reports. Let us
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