What’s a man? Or, indeed, a woman? Biologically, the answer might seem obvious. A human being is a(n) 【C1】______who has grown fr

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问题    What’s a man? Or, indeed, a woman? Biologically, the answer might seem obvious. A human being is a(n) 【C1】______who has grown from a fertilised egg which【C2】______genes from both father and mother. A growing band of biologists, 【C3】______, think this definition incomplete. They【C4】______people not just as individuals, but also as ecosystems. In their view, the descendant of the fertilised egg is【C5】______one component of the system. The others are trillions of bacteria, each equally an individual, 【C6】______are found in a person’ s gut, his mouth, his skin and all of the crevices and orifices that exist in his body’s surface.
   A【C7】______adult human harbours some 100 trillion bacteria in his gut alone. That is ten times as many bacterial cells as he has cells【C8】______from the sperm and egg of his parents. These bugs, moreover, are【C9】______. Egg and sperm provide about 23, 000 different genes. The microbiome, as the body’s commensal bacteria are collectively known, is reckoned to have around 3million.【C10】______, many of those millions are variations on common themes, but equally many are not, and even the number of【C11】______that are adds something to the body’ s genetic mix.
   And it really is a system, for evolution has【C12】______the interests of host and bugs. In exchange for raw materials and shelter the microbes that live in and【C13】______people feed and protect their hosts, and are thus integral to that host’s well-being. Neither wishes the other harm. In bad【C14】______, though, this alignment of interest can【C15】______. Then, the microbiome may misbehave in ways which cause disease.
   That bacteria can cause disease is no【C16】______. But the diseases in question are. Often, they are not acute infections of the【C17】____ 20th-century medicine has been so good at dealing with. They are, rather, the chronic illnesses that are now, 【C18】______in the rich world, the main focus of medical attention.【C19】______, from obesity and diabetes, via heart disease and asthma to neurological conditions such as autism, the microbiome seems to play a(n) 【C20】______role.
【C13】

选项 A、with
B、on
C、up
D、at

答案B

解析 本题考查介词辨析。此处that live in and______people明显为定语从句,修饰先行词microbes,意为“存在于人体内或人体表面的细菌”。on有“在……上面”之意,符合题意,故B.on为正确答案。live with“与……一起生活”,live up一般与to连用表示“符合”,live at“住在”,均不符合题意,故排除。
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