22. You mustn’t _____(leave) until I_____(come) back.

21. I went to bed after I ____(finish) the letter to my father.

20.If he is busy, he _____(not come ) to your birthday party.

19.I’m weak in _____(learn) geography.

18.If there____(be) a lot of traffic , you must wait.

17.If you _____(not hurry) , you’ll miss the train.

16.My mother makes me _____(play) the piano for an hour every day.

15.It’s dangerous _____(cross) the street when the traffic _____(be) busy.

14.I telephone him ____(fix) the radio for me.

13.It’s good for you ____(take) more exercise.