20.　 You can do your homework today or you can do it tomorrow.

______ today _______ tomorrow _______ OK for you to do your homework.

19.　 He left here two weeks ago.　 He has _____ ______ _______ here for two weeks.

18.　 Jim came into the library half an hour ago.

It _____ half an hour since Jim _______ _______ the library.

17.　 Ron did best in protecting the environment.

_______ ________ did better than Ron in protecting the environment.

16.　 Mr. Smith began to teach English at the age of twenty.

Mr. Smith _______ _______ English _______ he was twenty.

15.　 Remember to ring me up as soon as you get to London.

_______ _________ to give me _____ ______ as soon as you _______ London.

14.　 It’s a long time since we met last.　 We ______ _______ each other for a long time.

13.　 I’m too busy to go to the cinema tonight.

I have _______ ________ to go to the cinema tonight.

12. We spent twenty minutes cleaning the room yesterday.

It ______ us twenty minutes _______ ________ the room yesterday.

10.　 The film began ten minutes ago. 　The film ____ _____ ____ for ten minutes.

11　 We must keep our classroom clean.　　 We don’t ______ our classroom _______.