He has two pets. One is a dog, ______ is a cat.
It’s necessary _______ us to keep our pets clean every day. [ ]
Put your new clothes. Let’s go to the party. [ ]
Look at that girl! Is it Susan? –No, it _______ be hers. She has gone back to her hometown.
The light is on in Mr. Green’s room. He _______ be at home.