Direction：Read the following passage and answer the questions according to the imfomation you get in the passage and the required words limit．

　　Agricultural scientists in the United States have put a copy of a human gene into pigs, sheep and rabbits．They report that the gene seems to be working in some of the animals．The gene that the scientists are using controls the production of human growth hormone(荷尔蒙), a chemical necessary for growth．

　　They are using the human gene because it has been more closely studied than any other growth gene．The scientists hope their work will someday result in food animals that grow faster and larger or produce more milk or eggs．The research is being done by scientists at the University of Pennsylvania, the University of Washington and the United States Department of Agriculture．The scientists put copies of human growth hormone into the fertilized(受精的)eggs of the female animals．When baby animals were born from the eggs, the scientists looked for evidence that the human gene had become part of the animal’s genetic material．They examined almost 200 baby pigs and found the gene in 20 of them．They found it in 28 of more than 200 rabbits, but it was in only one of 73 baby sheep．The scientists said they found the human growth chemical produced by the gene in some of the animals．

　　It is too soon to know if the animals will pass the human growth gene into their young, proving that the gene has become part of their genetic material．Similar research with mice two years ago produced a new kind of mouse that is two times larger than normal．The scientists hope the same thing will happen with farm animals．They say their research will permit other gene transplants that can give animals defense against diseases, or let them live in very hot or very cold places．American farmers already use chemical hormones to increase the size of cattle and the amount of milk they produce．But they have to put the hormones into the cows．If the gene transplants are fully successful, the cow’s body will produce growth hormone．

1．How many kinds of animals have scientists put copies of human gene into?(no more than 1 word)

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2．Why do the scientists do such a research?(no more than 15 words)

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3．How does the gene work in the growth of animals?(no more than 8 words)

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4．What can we learn about the research with mice?(no more than 13 words)

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