29. The secretary worked late into the night , ________ a long speech for the president .

　　 A. to prepare　　　　　　 B. preparing　　　　 C. prepared　　　　　　　　 D. was preparing

28．I regretted _____ that to her. 　A. having said B. to have said　　　　　　　 C. to say　 D. /

27．He had no difficulty _____ the problems. 　A. working out　 B. having worked out　　　 C. to have worked out　　　 D. to work out

26．We are both looking forward to _____ next week. 　A. going on vacation 　　　　　　 B. go on vacation 　C. be going on vacation　　　　　 D. have gone on vacation

25．Only one of these books is _____. 　A. worth to read 　B. worth being read　 C. worth of reading 　D. worth reading

24．Don't forget _____ this book to John when you see him. 　A. to return 　　　 B. returning　　　　 C. return 　　　　　　 D. to returning

23．The scientist suggested ____ the experiment in a different way.

　 A. do　 B. to do　 C. doing　 D. done

22.Seeing is _________.

　　 A. to believe　 B. believing　　　 C. believed　 D. being believed

21.__________ clean is a safeguard against disease.

　　 A. To be keeping　 B. Kept　　　 C. Keep　　　 D. Keeping

20.What about _________ to the concert with us ?

　　 A. we go　　 B. we going　　 C. going　　　 D. to go