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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. "
Dr. Navara reached her conclusion through______.
选项 A、comparing data
B、field study
C、conducting a survey
D、map reading
答案A
解析 此题是一道细节推断题，考查考生根据文章内容和相关重点细节进行总结归纳和推断的能力。问题问纳瓦拉博士是通过什么得出结论的。文章第三段介绍纳瓦拉博士是利用多个国家纬度数据、10年的出生性别比例数据以及白昼长度和温度的年度变化数据进行统计分析得出结论的。所以，本题的答案应该是A，比较数据的方式。选项B：现场研究、田野调查，文章中没有提及与此相关的信息；C：进行调查，文中没有提到纳瓦拉博士做调查的相关信息；D：阅读地图、航图测读，文章中没有提及此方法。这三个选项均为干扰项。
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