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

---Someone is knocking at the door. Who may it be? ---It ______ be Tom. He is still in the school.

According to the factory safety rules, all accidents _____ be reported to the safety officer.

 When I lived with my roommates in the university, we ________ often talk into the night.

 I’m as busy as a bee; ________ you bother me with so many questions now?