One way that scientists learn about man is by studying animals．In this lab, the scientists are studying the relationship(关系)between diet(饮食)and health．They are studying the relationship between the amount(数量)of food the mice(老鼠)eat and their health．The mice are in three groups．All three groups are receiving the same healthy food．The first group is eating one cup of food each day, the second group is eating two cups, and the third group 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 a little thinner．But they are more active．Most of the day, they are running, playing with one another．Also, they are living longer．Mice usually live for two years．Most of the mice in this group are still alive after three years．

　　The second group of mice is healthy, too．They are active, but not as active as the thinner mice．They are only living about two years．

　　The last group of mice is receiving more food than than the other two groups．Most of the day, these mice are eating of 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．They are sick more often than the other two groups．

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　　Cats are the most popular pets among Americans．So it is not surprising that there are a lot of expressions about cats．Some cats like to catch small birds, like canaries(金丝雀)．If someone looks very proud and satisfied with himself, we say“he looks like the cat that ate the canary．”

　　Sometimes, a cat likes to play with a small animal it catches．So if you“play cat and mouse”with someone, it means that you change between different kinds of behavior when dealing with another person．For example, a girl might offer something sweet to her little brother and then take it away when he reaches for it．

　　Americans might say that something is“the cat's miaow”or“the cat's pajamas(睡衣)”to describe something that is the best or finest．“A copycat”is someone who acts just like someone else or copies another person's work．“A fat cat”is a person with a lot of money．

　　If you tell about something that is supposed to be a secret, we say you“let the cat out of the bag”．If you are not able to speak or answer a question, someone might ask you if“the cat has got your tongue(舌头)”

　　Have you ever watched children in a classroom when their teacher leaves for a few minutes?“When the cat's away, the mice will play”means people sometimes act badly when there is no supervision(监管)．

　　You may have heard the expression“curiosity killed the cat”．This means caring too much about things that are not your business might cause problems．

　　If you have ever had cats as pets, you know it is difficult to train them or to get them to do something．Cats are not like Sheep or cows that can be moved in a group．So we say a difficult or impossible job is like“herding(放牧)cats”

阅读理解

　　Cats are the most popular pets among Americans．So it is not surprising there are many expressions about cats．Do you know any of them? Now let me introduce some to you．

　　Some cats like to catch small birds, like canaries．If someone looks very proud or satisfied with himself, we say he looks like the cat that ate the canary．

　　Sometimes, a cat likes to play with a small animal it catches．So if you play cat and mouse with someone, you change between different kinds of behavior when dealing with another person．For example, a child might offer something sweet to her little brother, and then take it away when reaches for it．

　　A cat will often catch a small animal and present it to its owner．The saying that looks like something the cat dragged in describes something in bad condition．

　　A fat cat is a person with a lot of money．

　　There are many other expressions about cats in America．How interesting! Which kind of cat are you, or which kind would you like to be? [来源：Z。xx。k．Com]