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

—I didn't go to see the doctor yesterday.—But you ________.

---Could I have some snacks between meals, mum?---No, you __________.

—Bob, where is Linda?—She          be in the library, but I am not sure.

—Why, my new computer is rubbish! Five hours has passed and it still hasn’t finished the downloading. —Don’t worry. You know, sometimes the Internet ________ be very slow.