He smokes three packs of cigarettes a day,which definitely doesharm to his health 这句话为什么用does

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He smokes three packs of cigarettes a day,which definitely does
harm to his health 这句话为什么用does

which引导的非限制性定语从句是用来修饰前面的整个一个句子,并不是一个名词,所以用单数does.

他每天抽3包烟,‘这’对他的健康有很大伤害。
which指代‘这’,也就是抽3包烟这件事,所以是单数。

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