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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 细节理解题。从第二段的“…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”可知，与出生婴儿的性别比例有关的社会、经济和生物因素，具体包括：战争、经济压力、年龄、饮食、选择性流产和其他因素。根据关键词Dr．Navara，我们返回到第三段找到相应的定位句：Kristen J．Navara of the University ofGeorgia…atbirth and annual variations in day length and temperature．由此可确定Kristen的关注点是latitude和data。根据以上内容，我们可确定答案为C。A项并未提及，B和D不是Navara关注的内容。
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