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  3. More boys than girls are born all over the world, but a new study has found that the closer people live to the equator(赤道), the

More boys than girls are born all over the world, but a new study has found that the closer people live to the equator(赤道), the

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问题     More boys than girls are born all over the world, but a new study has found that the closer people live to the equator(赤道), the smaller the difference becomes. No one knows why.
    The imbalanced sex ratio at birth has been known for more than a hundred years, and researchers have found a large variety of social, economic and biological factors that relate to the sex ratio at birth—war, economic stress, age, diet, selective abortion and more. But latitude(纬度)is a natural phenomenon, unaffected by cultural or economic factors.
    To look at the effect of latitude, Kristen J. Navara of the University of Georgia used the latitude of the capital city in 202 countries, as well as 10 years of data on sex ratio at birth and annual variations in day length and temperature. Dr. Navara performed a statistical analysis which showed that there was a significant relation between sex ratios in favor of boys and latitude. African countries produced the lowest sex ratios—50. 7 percent boys—and European and Asian countries had the highest with 51. 4 percent.
    There are some possible explanations, but none entirely satisfactory. It could be that there is some survival value in producing more girls in warmer regions, but it is unclear what this might be. There may be genetic or racial differences that could explain it, but the connection persists over so many varied populations that this seems unlikely. Mice also produce more male offspring during shorter days or colder weather, but the reasons in these animals are just as mysterious as they are in humans.
    "There’s a possibility that humans might be responding to factors they were programmed to respond to a long time ago—not cultural or socioeconomic, but climate and things like latitude," Dr. Navara said. "What’s interesting is that we may be seeing something that connects us with our animal ancestry. "
Out of all the influencing factors of birth ratio, Dr. Navara focuses on______.
选项 A、culture
B、economy
C、latitude
D、stress
答案C
解析 此题是一道细节判断题，考查考生根据文章内容和相关重点细节进行分析判断的能力。问题问在所有影响出生率的因素中纳瓦拉博士关注的是什么。利用查阅式阅读法，我们可以在第三段中找到相关信息。这部分指出：为了研究纬度的影响，佐治亚大学的克里斯汀.J.纳瓦拉采用了202个国家首都城市的纬度数、10年的出生性别比例数据以及白昼长度和温度的年际变化数据。纳瓦拉博士进行了统计分析，结果表明在有利于生男孩的性别比例和纬度之间存在一个显著的关系。由此我们可以推断出本题的答案应该是C，纬度。选项A：文化；B：经济；D：压力，文章中未提及；这三个选项中虽然文章提到了文化和经济因素，但是不是纳瓦拉博士关注的焦点，所以均为干扰项。
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