Question

—Oh, there's someone knocking at the door. —______ must be that naughty boy.

—Oh, there's someone knocking at the door. —______ must be that naughty boy.
其中，为什么用It？不用He?????

Answer 1

因为不知道是谁。所以不能用he, or she。it 可以表示人物。

英汉词典的解释：
it：〔指心中记着或成为问题的人物、事情和行为〕。 Go and see who it is. 去看看是谁？ It's me. 〔口语〕是我 (＝It is I.)。 Oh, it's you! 哦，是你呀! It's the girls having their rehearsal. 是女同学在排戏。

Answer 2

表示猜测的，不明对象的猜测~

Answer 3

It 是固定用法 你不知道那个人是男是女

Answer 4

It,