—David，is that man your Chinese teacher?—It___________ be him．He’s having a meeting． 

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

—The research on the new flu virus vaccine is challenging and demanding. Who do you think can do the job?     —_______ my students have a try?

—Look at that girl! Is it Susan?—No, it _______ be her. She has gone back to her hometown.

She __________ be here. I saw her come in.