who is knocking on the door ___must be Helen.
问题描述:
who is knocking on the door ___must be Helen.
答
It must be Helen.
一定是海伦.
敲门的时候,这是固定用法.
例A:Who is that?
B:It is Eva.
A:(主人问)
B:是Eva(回答的人说)
)