复合题

The aging process may not be the result of a rigid genetic program that in itself dictates longevity. On the contrary, what we see as maximum life span may simply be the complex and indirect result of multiple traits in the organism that are internally tied to normal development. In other words, it is not that the body is somehow pre-programmed to acquire gray hair, wrinkles, or diminished metabolic（新陈代谢的） functions. Rather, these signs of aging are simply telltale side effects of activities of the organism.

Consider the analogy of an “aging car”. Suppose a distinctive “species” of automobile were designed to burn fuel at a fixed temperature with an efficient rate of combustion（燃烧） . That specific rate of combustion is required for appropriate acceleration, cruising speed, fuel mileage（油耗） and so on. But, when the car functions in this way over a period of time, the car also, of necessity, produces certain emission by-products that, over time, begin to clog the cylinders, reduce automotive efficiency, and lead to the breakdown and final collapse of the machine.

In the case of the human “car”, it could be the burning oxygen in normal metabolism generates harmful by-products in free radicals that prove toxic to the organism. What we see here may be a basic trade-off: oxygen is essential for life yet harmful to our eventual well-being. In this view, the human “car” is not intentionally designed to accumulate toxic emissions in order to collapse. But there seems to be no way for the car to function at optimum levels without the destructive by- products.

But suppose we could find some special “fuel additive” that eliminates toxic emissions. Would we then have an “immortal” car? Probably not. Changing the fuel used in your car won’t prevent accidents, nor would any fuel additive prevent rusting or the wearing down of springs and shock absorbers. The human “car” analogy, of course, is misleading, because an organism, unlike a manufactured object, has a capacity for repair and self-generation, at least up to certain point. The whole question about why we grow old is finding out why that capacity for self-repair ultimately seems unable to keep up with the damage rate: in short, why aging and death seem to be universal.

单选题 From the passage, we learn that _____.
【正确答案】 C
【答案解析】根据文章第一句“The aging process may not be the result of a rigid genetic program”即衰老可能并非严格按照基因程序所带来的结果。 C项与文意相符。
单选题 The example of the “aging car” is used to make the point that _____.
【正确答案】 A
【答案解析】根据题干中的“aging car”定位至文章第二、 三段， 作者指出“…when the car functions in this way over a period of time, the car also, of necessity, produces certain emission by-products that…”由此可推断aging其实是整个人生过程中的by-products（ 附带产生的结果， 副产物） ，即选项A正确。
单选题 A “basic trade-off” (Line 3, Para. 3) is a process _____.
【正确答案】 D
【答案解析】原文中提到“What we see here may be a basic trade-off: oxygen is essential for life yet harmful to our eventual well-being”氧气既是必需的却又对我们有害， trade-off指的是两种对立关系之间的权衡， 故D项符合题意。
单选题 Which of the following statements is true according to the passage?
【正确答案】 C
【答案解析】根据文章第一段“…maximum life span may simply be the complex and indirect result of multiple traits in the organism”可知长寿是由多种不同因素决定的， C与之相符， 故选C。
单选题 The “human car” analogy is faulty in the way that _____.
【正确答案】 B
【答案解析】文章最后一段提到“The human ‘car’analogy is misleading because an organism, unlike a manufactured object, has a capacity for repair and self-generation, at least up to certain point.”即这一类比有缺陷， 因为人类机体并不像“car”一样， 它是拥有一定的自我修复和再生的能力的，故B项符合文意。