Do you know the man _who_ is reading the book over there?
Yes, he's Mr. Green , our PE teacher.
你认识正在那边看书的那个人么?
是的,他是格林先生,我们的体育老师.

who 引导定语从句,先行词是the man, 并在定语从句中做主语,意思是先行词the man那个人.

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