Who is knocking at the door?I think ___ is the postman?A、it

Who is knocking at the door?I think ___ is the postman?A、it someone is knocking at the door （）i go and see who it is A s someone is knocking at the door .（）i go and see who it is A 请看下面的句子：Who is knocking at the door?I think (it) is Li Lei.为 someone is knocking at the door.who [ ]it be? ---someone is knocking at the door.Who _____ it be? someone is knocking at the door,who is it? A this is a polic who is knocking at the door? 1.----Who is knocking at the door Listen!Who is knocking at the door? who is knocking at the door?it is ()me还是i呢?求理由 --who's that at the door?--____ is a postman.