24. The ground is 　　　　with 　　　　　leaves.　

　 A. covering, falling 　　　 B. covered, falling　　 C. covered, fallen 　 　　 D. covering, fallen

23. The library's study room is full of students 　　　　　for the exam.

　 A. busily prepared　 B. busy preparing　　　　 C. busily prepare 　 　 D. are busily preparing

22. The scientists were waiting to see the problem 　　　　.　

　 A. settle　　 　　 B. settled　　 C. to settle　　 　　　 D. settling

21. The foreigner tried his best, but he still couldn't make his point 　　.

　 A. understand　 　　　 B. understanding 　　 C. to understand 　 　 D. understood

20. People 　　　　in the city do not know the pleasure of country life.

　 A. live　　 　　　 B. to live　　 　 C. lived　　 　 D. living

19. The 　　　　　price will save you one dollar for each dozen.

　 A. reduce　　 　 B. reducing　　 　　 C. reduced　　 　　　 D. reduces

18. The student corrected his paper carefully, 　　　　the professor's suggestions.　

　 A. follow　 　　　 B. following　 　　 C. followed　 　　 D. being followed

17. He went from door to door, 　　　　　waste papers and magazines.　

　 A. gathering　　　　 B. gathered　 　　 C. gather　　 D. being gathered

16. 　　　　 　the office, the foreign visitors were shown round the teaching building. 　

　 A. Having shown　 　　 B. Showing　 　 C. Has shown　 　　 D. Having been shown

15. With winter 　　　　　on, it's time to buy warm clothes.　

　 A. came　　 　　 B. comes　　 　 C. come　　 　 D. coming