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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. "
What is the purpose of the passage?
选项 A、To tell a mysterious story.
B、To report a scientific experiment.
C、To explain an interesting phenomenon.
D、To argue for a viewpoint.
答案C
解析 此题是一道考查考生根据文章整体内容进行总结归纳和分析概括的能力。问题问本文的写作目的是什么。利用浏览式阅读，我们发现文章重点围绕如何解释人类男女出生性别比例差异来写的。文章先介绍一种现象：世界各地出生的男孩比女孩多。但是一项新的研究发现，人们住得越靠近赤道，其差异就会变得越小。接下来作者通过叙述佐治亚大学纳瓦拉博士的研究发现分析了纬度和气候等非文化社会因素对男女出生性别比例的影响。最后作者指出，人类出生性别比例的差异仍然有许多无法解释的方面，有待于进一步研究。由此我们可以概括推断出本文的写作目的是解释一种现象，探讨该现象背后的原因。所以，本题的正确答案应该是C，解释一种有趣的现象。选项A：讲述一个神秘的故事；B：报道一个科学实验；D：论证一个观点。这三个选项都不是本文的写作目的，均为干扰项。
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