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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.  
It can be inferred from the passage that_____.
选项 A、some have two short alleles, and others have two long ones
B、different races may have different propensities for happiness
C、the notion that human personality is a blank slate is strengthened
D、those with two short alleles were more likely than those with one long allele
答案B
解析 根据题干关键词定位到整篇文章。第四段前三句提到“血清素与情绪调节有关……血清素转运体基因有两种变体：长型和短型”，根据第五段中“不同的种族有不同数量的长型基因”可推断出B项“不同种族的幸福倾向不尽相同”。A项缺少了一种搭配，即“有些人长型短型等位基因各一个”；第二段首句提到“性格……是遗传的，这个观点正变得越来越明确”，所以C项观点的说服力应该是逐渐减弱；D项过度推断，均排除。
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