第一节：单项选择。（共15小题，每小题1分，满分15分）
21.It was about 500 years ago the first clock with a face and an hour hand was made.
A. that B. until C. before D. when
22. the population of the developing country?
A. How many are B. How much is C. What’s the number of D. What’s
23. is generally accepted, economic growth is determined by the smooth development of the production.
A. What B. That C. It D. As
