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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".
What does the passage mainly talk about?
选项 A、Your compatibility genes make you unique as well as affecting all parts of your life.
B、Donor skin grafts failed because the recipient’s immune system recognized the grafted skin as foreign and killed it.
C、Our appearance, lifestyle and career path may make us feel unique, so that grafted skin can not live in our body.
D、Our immune systems are able to attack a great diversity of molecules, especially those of pathogens.
答案A
解析 该题需要通读全文，明确文章的中心思想。文章主要是为了说明为什么我们的免疫系统能识别哪些是自己的组织细胞，哪些是别人的。主要是因为亲和基因让我们独一无二，所以选出正确答案A。其他几个选项所表述的内容在文章中都有论述，但不能概括文章的主旨。
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大学英语四级

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