单选题
Pressure and Pregnancy

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 falling recently. Several theories have been put forward to explain these observations. Some argue that smoking plays a role, others say 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.
Strange as it might seem, the terrorist attacks of September 11th 2001 shed light on the enigma. Studies noting the sex of babies conceived in New York during the week of the attacks found a drop in the ratio of males to females. That is consistent with earlier studies, which revealed a similar 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 1989 and 1992. 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, failing suggests that rich women"s lives may be more stressful than they used to be.
单选题 The author begins the passage by ______.
【正确答案】 A
【答案解析】[解析] 细节考查题。文章一开始就提出问题,许多人的解释都不能被大型的研究所证明,现在又有新的论点,就是压力的作用。接下来的几段就是对这个论点的证实。可见,作者是以提出一个论点的形式来开始这篇文章的。故正确答案为A。
单选题 The ratio of giving birth to a boy is falling in rich countries because ______.
【正确答案】 B
【答案解析】[解析] 细节考查题。题干问富裕国家目前男孩出生率下降的原因。答案参见最后一段最后一句,目前这个比率下降可能是因为富裕国家妇女现在承受的压力要比以前大,但是没有说明有新的压力出现。故正确答案为B。
单选题 Which of the following can explain Dr. Obel"s opinion that the ultimate cause is adaptive rather than pathological?
【正确答案】 C
【答案解析】[解析] 细节考查题。答案参见第五段,在资源紧缺的男性竞争社会中,弱小的男性更容易被边缘化,被淘汰,而女性则不存在这个问题,所以面对这种压力,妇女生育孩子时会选择将男婴流产,这是一种适应环境的做法。
单选题 Women in the hunter-gatherer societies are more likely to give birth to daughters because ______.
【正确答案】 D
【答案解析】[解析] 细节考查题。在原始狩猎社会中,女孩出生率较高的原因是妇女生育时面临的压力。选项D符合题意。选项A明显错误;选项B并不是题干的原因;选项C与原文相反,故均可排除。
单选题 From this passage, we may draw a conclusion that ______.
【正确答案】 B
【答案解析】[解析] 主旨题。本文主要讲述了压力对于婴儿性别的影响,分别用一些数据和事实证明突发压力和慢性压力都有一定的影响,从中可以得出结论,就是突发压力与急性压力都会使女孩的出生率高一些。故正确答案为B。