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Because children's brain and behavioral disorders, like hyperactivity and lower grades, can also be linked to social and genetic factors, it's tough to pin them on exposure to specific chemicals with solid 33 statistical evidence, which is what the EPA re
2015年12月六级真题（第一套）阅读 Section A
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Some of the statistical generalizations may be positive and some groups have reputations for being smart, for being loyal, for being brave, for all sorts of things that are not at all negative.
2017年12月六级真题（第二套）听力 Section C
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The studies also ran up against many methodological challenges, the biggest of which centered on the old statistical saying, "Correlation does not equal causation."
2018年12月六级真题（第一套）听力 Section C