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  3. Why Do We Not Live Forever? The human body is composed not of perishable materials like wood or metal, but of living cells t

Why Do We Not Live Forever? The human body is composed not of perishable materials like wood or metal, but of living cells t

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问题             Why Do We Not Live Forever?
    The human body is composed not of perishable
materials like wood or metal, but of living cells
that can grow and replenish themselves. However if the body’s             【M1】______
individual units are renewable, why do we not live forever?
Theologians explain that Adam and Eve were refused                        【M2】______
mortality and expelled from Eden because they disobeyed God.              【M3】______
Evolutionary biologists hold that natural selection favors
genes that promote having many offsprings to those that                   【M4】______
might insure longer life. In their view, life span is a trade-off         【M5】______
between fertility and longevity, and infinite life would be allied                                with childlessness and rapid extinction.
A chance discovery that a Texas biologist has provided a                  【M6】______
different kind of explanation. The biologist, Dr. Lawrence
Donehower of the Baylor College of Medicine in Houston, has
found that age seems to be a necessary cost of suppressing                【M7】______
cancer.
The finding concerns with an intensively studied cellular                 【M8】______
agent that is the body’s first line of defense
against tumors. The agent is known to biologists with the                 【M9】______
humble name of p53—p for protein, 53 a measure of its weight.
In fact, p53 is one of most important hubs in the living cell’s vast      【M10】______
network of interacting components. Many circuits that monitor
different aspects of the cell’s integrity report back to p53
【M7】
选项
答案将age改成aging。
解析 age作“衰老”时是动词，显然要用动名词形式才可以作从句中的主语。age作名词表示“年龄、年代”等，与上下文意思不符。
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