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  3. During the Second World War, doctors tried to save severely burned pilots with grafts of donated skin. The grafted skin looked g

During the Second World War, doctors tried to save severely burned pilots with grafts of donated skin. The grafted skin looked g

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问题    During the Second World War, doctors tried to save severely burned pilots with grafts of donated skin. The grafted skin looked good for a few days, but then withered and died. Studies led by Peter Medawar—who won a 1960 Nobel Prize for his work—found that grafts of an individuals own skin did work, while those of a donor did not. We now know that the donor skin grafts failed because the recipient’s immune system recognized the grafted skin as foreign and killed it. The same process leads to the rejection of donated organs. But how does our immune system learn what is self and what is foreign?
   As immunologist Daniel Davis explains in The Compatibility Gene, it is all down to specific genes—formally known as the major histocompatibility complex genes. Although our appearance, lifestyle and career path may make us feel unique, we are actually always one of a group: it is only our compatibility genes that define us as true individuals. Davis provides a well-written and easy-to-read account of the sometimes complicated biology behind the crucial genes that affect our lives so profoundly.
   From early on in the evolution of life, individual cells—and later multicellular organisms— developed the ability to recognize that which was the same as them, and that which was different. Davis recounts how, when we are growing as fetuses, our compatibility genes train the immune system to recognize our own cells and tissues as "self" and so, in healthy people, they know what not to attack. Our cells are identified by the presence of unique surface molecules, coded for by the compatibility genes.
   Meanwhile, our immune systems make antibodies. These are randomly generated in a kind of lottery, which means they will be able to attack a great diversity of molecules, especially those of pathogens. By chance, though, a few of these antibodies will also match the compatibility-gene molecules on our own cells. Leaving such antibodies around would be suicide—literally. To stop this, Darwinian-style selection comes into play within the immune system, eliminating any cells that produce antibodies matching "self".
Why did the grafted skin withere and die after a few days?
选项 A、Because a person’s immune system identifies the grafted skin which comes from other people.
B、Because people have different immune systems, and these immune systems can not be blended together.
C、Because the special features of grafted skin can not be adapted by the recipients.
D、Because the recipients do not have powerful immune system for fighting diseases.
答案A
解析 根据题干可以将该题定位至文章第一段，第一段指出We now know that the donor skin grafts failed because the recipient’s immune system recognized the grafted skin as foreign and killed it，因此可以很快选出A选项，A中的identifies是recognized的同义替换。B、C和D选项都是对文章相关信息的曲解。
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大学英语四级

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