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  3. As any human being knows, many factors govern whether people are happy or unhappy. External circumstances are important: employe

As any human being knows, many factors govern whether people are happy or unhappy. External circumstances are important: employe

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问题     As any human being knows, many factors govern whether people are happy or unhappy. External circumstances are important: employed people are happier than unemployed ones and better-off people than poor ones. Age has a role, too. But personality is the single biggest determinant: extroverts are happier than introverts, and confident people happier than anxious ones.
    That personality, along with intelligence, is at least partly heritable is becoming increasingly clear; so, presumably, the tendency to be happy or miserable is, to some extent, passed on through DNA. To try to establish just what that extent is, a group of scientists examined over 1, 000 pairs of twins from a huge study on the health of American adolescents. They conclude that about a third of the variation in people’ s happiness is heritable.
    But while twin studies are useful for establishing the extent to which a characteristic is heritable, they do not finger the particular genes at work. One of the researchers, Jan-Emmanuel De Neve, of University College, London, and the London School of Economics, has tried to do just that, by picking a popular suspect—the gene that encodes the serotonin-transporter protein, and examining how variants of that gene affect levels of happiness.
    Serotonin is involved in mood regulation. Serotonin transporters are crucial to this job. The serotonin-transporter gene comes in two functional variants—long and short People have two versions(known as alleles). The adolescents in Dr. De Neve’ s study were asked to grade themselves from very satisfied to very dissatisfied. Dr. De Neve found that those with one long allele were 8% more likely than those with none to describe themselves as very satisfied; those with two long alleles were 17% more likely.
    Which is interesting. Where the story could become controversial is when the ethnic origins of the volunteers are taken into account. All were Americans, but they were asked to classify themselves by race as well. On average, the Asian Americans in the sample had 0.69 long genes, the black Americans had 1.47 and the white Americans had 1.12.
    There is growing interest in the study of happiness, not just among geneticists but also among economists and policymakers dissatisfied with current ways of measuring humanity’s achievements. Future work in this field will be read avidly in those circles.  
By examining over 1,000 pairs of twins, scientists intend to confirm the extent of that______.
选项 A、external circumstances govern happiness
B、personality determines happiness
C、genes identify happiness
D、age affects happiness
答案C
解析 根据题干关键词定位到第二段。该段第二句指出“为了确定程度有多大，一组科学家……对1 000对双胞胎进行了测试”，句中的that指代的是上句末提到的“一个人感到幸福还是悲伤的倾向可能是由基因传递的”，综上所述，科学家做测试的目的是“确定基因到底在多大程度上决定幸福”。故C项为正确答案。A、B、D项的说法均正确，但是并不是科学家对1 000对双胞胎进行了测试的原因，不符合题意，故排除。
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