-Someone’s knocking at the door. Is it your mother?-No, dad. It _____be mom. I saw mom ____in the bedroom just now.
Peter, you should leave the light when you’re out.
I think it’s unusual thing to find a UFO.
The young lady________ is talking with our teacher comes from America.
Waste paper mustn’t _______. We should keep our environment clean.
Come on! You will catch up with others _______ you work hard.