Who is that at the door ？

Who is that at the door? Who is that at the door ？ --who's that at the door?--____ is a postman. Who's that at the door who is knocking at the door? 1.----Who is knocking at the door Listen!Who is knocking at the door? —There is a knock at the door.—---------------?A.who is that 语法,( ) 1 Who's that at the door?____ is the postman.A.She B. Who's that at the door?____ is the postman.A.She B.This C.It -Who ＿＿it be that is knocking at the door -It＿＿b 单句改错 who is the men knocking at the door