英语选择Some one is knocking at the door.who _it be? a can b may

Someone is knocking at the door,but who can （ ）be.A one B he Who is knocking at the door?---_____ may be Mary.A.She B.He Someone is knocking at the door.Who can it be?的回答.A.Nothing Someone is knocking at the door,but who can____ be? someone is knocking at the door.who [ ]it be? --Listen! Someone is knocking at the door. Who _____it be? ---Listen! Someone is knocking at the door. Who _____it be? ---someone is knocking at the door.Who _____ it be? 单项选择,懂的来,( ) Who is knocking at the door?----- ____ is me.A. who is knocking at the door?i suppose------must be bob.A.the -Who ＿＿it be that is knocking at the door -It＿＿b who is knocking at the door?