19.　 A lot of water ___(waste) every year. It’s a serious problem.

18.　 　The car__ hit a tree when it____(run) at the speed of 60 miles an hour.

17.　 Do you mind my____(open) the widow?

16.　 I’m sorry to have kept you ____(wait) so long .

15.　 The workers ___(cut) down the trees and the trucks____ (arrive)an hour ago.

14.　 We ____(play) football if it____(be) fine next Sunday.

13.　 Yesterday Miss Gao ____(tell) us she ____(teach) Chinese three years ago.

12.　 Just wait and ___(not cross) the street until the traffic lights___(turn)green.

11.　 By the time my parents reached home. I___(cook)the dinner already.

10.　 Jim often ____(go) there at six last term.