第二部分：英语知识运用（共两节，满分45分）
第一节：单项填空（共15小题；每小题1分，满分15分）
从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21. As is known to all, ______ great scientific achievements may have ______ positive effect on our life as well as society.
A. /; a B. the; a C. the; / D. /； /
22. Selecting a digital camera for personal use is no easy task because technology ______ so rapidly.
A. is changing B. has changed
C. will have changed D. will change
23As soon as I was on _______, I began to have second thoughts about leaving.
A. abroad B. broad C. aboard D. board
