What attitudes toward American life and toward racial differences are assumed in the text?

在其内容中对美国生活和种族差异作了哪些假设？

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The results were the same even after the researchers controlled for factors like age and racial differences.

研究者按照年龄和种族分类后仍然得到相同的结果。

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What the eye sees as racial differences - between Europeans and Africans, for example - are mainly a way to adapt to climate as humans move from one continent to another.

我们眼中看到的人种差异，例如欧洲人与非洲人的差异，主要是人类从一个大陆向另一个大陆迁移时为适应气候所产生的。

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Many complicating factors, say Clark and others, further taint survey results, including geographical, cultural and racial differences among patients.

FORBES: Why Rating Your Doctor Is Bad For Your Health

But, new research conducted by political scientists from the University of Chicago, suggest the effort could be compromised by huge racial differences on how to rebuild.

NPR: Study on Race and Rebuilding New Orleans

Unlike the USA, which has been a well-established federation on roughly the same geographic map over a century, EU is still a collection of states in an area where ethnic diversities, racial differences, ideology and economic antagonism have changed the map several times.

FORBES: EU: A Collection of Capricious Brides