My book, The House of Hales, is missing. Who ________ have taken it?

—The traffic is heavy now, so Mike       come late.—Let’s wait ten more minutes.

---Dad, must we wait until the light becomes green?---Yes,I’m afraid we      .That’s the traffic rule.

—Listen! Peter is singing in the classroom! —It _____ be him. He has gone back to his hometown.

---who______it be that is knocking at the door? ---It_______be Father, but I’m not sure.