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标题: 代词指代 [打印本页]

作者: fornow 时间: 2011-2-19 08:29
标题: 代词指代
53 Most vaccines are derived from weakened or killed strains of the same virus that they prevent, unlike smallpox vaccine, which is derived from a different virus altogether.

请帮忙解释一下THEY指代什么？

作者: coldice1205 时间: 2011-2-19 11:19
指代前面的vaccines

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