---There is somebody knocking at the door. Who________ it be?---I’m not sure. It ________ be a postman.

—Must we clean the classroom now?—No ,you _______.

Michael       be a policeman, for he is much too short．

Some frightening pets _________ be kept home so that they won’t hurt others.

I am not feeling myself today! We ____ have drunk that much beer last night.