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  3. A boy or a girl? That is usually the first question asked when a woman gives birth. Remarkably, the answer varies with where the

A boy or a girl? That is usually the first question asked when a woman gives birth. Remarkably, the answer varies with where the

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问题     A boy or a girl? That is usually the first question asked when a woman gives birth. Remarkably, the answer varies with where the mother lives. In rich countries, the chances of its being a boy are about 5 ％ higher than in poor ones. Equally remarkably, that figure has been felling recently. Several theories have been put forward to explain these observations. Some argue that smoking plays a role; others hold that diet may be important. Neither of these ideas has been supported by evidence from large studies. But new research points to a different factor: stress.
    Early studies revealed a shift in women who became pregnant during floods and earthquakes and in time of war. Moreover, a study carried out eight years ago by researchers at the University of Aarhus, in Denmark, revealed that women who suffered the death of a child or spouse from some catastrophic illness around the time they conceived were much more likely to give birth to girls than to boys.
    Taken together, these results suggest that acute stress to a woman at the time of conception shifts the sex ratio towards girls. However, Carsten Obel, a researcher at Aarhus who was not involved in the earlier study, wondered if the same might be true of chronic stress too. In a paper just published in Human Development, he shows that it is.
    Dr. Obel used a set of data collected between 2012 and 2015. During that period 8,719 expectant mothers were asked to fill in questionnaires that inquired, among other things, about their level of stress. Dr. Obel found that the more stressed a mother had been, the less chance she had of having given birth to a boy. Only 47％ of children born to women in the top quartile of stress were males. That compared with 52％ for women in the bottom quartile. Dr. Obel suspects the immediate cause is that male pregnancies are more likely to miscarry in response to stress than female pregnancies are, especially during the first three months. However, that is difficult to prove. More intriguing, though, is the ultimate cause, for he thinks it might be adaptive, rather than pathological.
    That is because the chances are that a daughter who reaches adulthood will find a mate and thus produce grandchildren. A son is a different matter. Healthy, strapping sons are likely to produce lots of grandchildren, by several women—or would have done in the hunter-gatherer societies in which most human evolution took place. Weak ones would be marginalized and maybe even killed in the cut and thrust of male competition. If a mother’s stress adversely affects the development of her fetus then selectively aborting boys, rather than wasting time and resources on bringing them to term, would make evolutionary sense.
    That, in turn, would explain why women in rich countries, who are less likely to suffer from hunger and disease, are more likely to give birth to sons. That this likelihood is, nevertheless, falling suggests that rich women’s lives may be more stressful than they used to be.
The author begins the passage by________.
选项 A、presenting an argumentation
B、explaining a phenomenon
C、raising a question
D、making a comparison
答案A
解析 本题无关键词，属于写作手法题，定位第一段。作者在文章一开始就指出富裕国家的女性生男孩的概率比贫穷国家高约5％，但目前这个概率在下降，有许多人给出自己的解释，但都不能被大规模的研究证明，而现在又有新的观点出现，就是压力(stress)的作用。接下来的几段都是对这个论点的证实。可见，作者是以提出一个论点的形式(presenting an argumentation)来展开这篇文章的，因此选项A属于全面概括，为正确答案。选项B属于无中生有，因为作者在开头没有解释(explain)。选项C属于无中生有，文章第一句A boy or a girl?的确是疑问句，但并不是说作者通过提问题(question)的方式开篇。选项D属于正反混淆，因为在文章开头只对富裕国家和贫穷国家进行了相反对比(contrast)，而选项D中的comparison强调的是相似点的比较。第一段：新的研究成果指出影响婴儿性别的另一个原因——压力。
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