Who is _at the door?She asked,but get no answer

Who is _at the door?She asked,but get no answer There was a stanger (stand)_at the door 单句改错 who is the men knocking at the door here is the door ------- .who is it the door ----- -----who is it 门铃响了,是谁呢? The boy who is standing at the door is my brother.who is 可以省略吗 Someone is knocking at the door,but who can____ be? Who is ___at the door?he she they it哪个 who is knocking on the door ___must be Helen. how is the man who lives next door我没搞懂为毛要有who%>_ The boy is my brother.The boy is standing at the door.合并:The boy who is standing at the door isThe boy is my brother.The boy is standing at the door.合并:The boy who is standing at the door is my brother.省略：The boy standing at the door is The teacher had John _at the door for an hour beacuse he was late for class.A.standB.to standC. 英语help!(请写清解析)The mother looked _at her son ,who was badly wounded.(sad sadly) who is knocking at the door?A.This is me knockingB.It's me. 为什么是is knocking：Who is knocking(knock) at the door?it's me. who is knocking at the door?it is ()me还是i呢?求理由 Someone is k_______ at the door.Go and see who it is. Someone is k_______ at the door.Go and see who it is. who is knocking at the door?i suppose------must be bob.A.the one B.it C.who D.he