题目内容：
Why do epidemiologists often study two groups of people?
参考答案：
答案解析：
不定项选择题：Why do epidemiologists often study two groups of people?
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In fall 2006, the National Basketball Association (NBA) star
In fall 2006, the National Basketball Association (NBA) started using basketball
In this part there are passages and one listing, each follow
In this part there are passages and one listing, each followed by five questions
The word unique in the passage is closest in meaning to
The word unique in the passage is closest in meaning to
People from many countries were drawn to the United States b
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