---  ________ have you kept the book ? --- Since last Month. I ________ return it to the library today or I can’t borrow one next time. 

—Dad, must I finish my homework today?—No, you ______. You may do it tomorrow.

 ---Who’s the man over there? Is it Mr. Black?--- It _________ be him. He’s much taller.

 My sister met him at the street yesterday afternoon, so he __________ your lecture.

—The speaker is a tall man with glasses.—Then it         be Mr. Smith, who is short and thin.