问题描述：
of whom用法
i sent invvitations to 80 people,of whom only 20 have replied 为什么不用i sent invvitations to 80 people,only 20 of these who have replied
i sent invvitations to 80 people,of whom only 20 have replied 为什么不用i sent invvitations to 80 people,only 20 of these who have replied
问题解答：
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