31.—Who is singing in the classroom — must be Susan .A

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31.—Who is singing in the classroom — must be Susan .A.She B.It C.This D.He
为什么选B?

it在这里的用法是明确身份,比如打电话时用的it's Tom,和这种用法是一样的.类似的还有 Was it youwho put these books on my desk?

31.—Who is singing in the classroom — must be Susan .A A:who is singing in the classroom listen,who is singing in the classroom? -Who is singing in the next room.-_ must be Marie A.It B.She Susan is singing in the classroom.对singing提问 Frank never see who is singing?it must be susan.为什么是用it Who is singing in the classroom?I want to know —Susan stays alone in the classroom and looks sad Who is in the classroom Someone is singing now.Who （）it be?A.must B.should C.can D.w He must be in the classroom ,___he? who is singing in the room?