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,并在答题卡上将该项涂黑。
例:A computer can only do ______ you have instructed h to do>
A. how B.
after
C. what
D.when
答案是C。
21. It is known to all that _____ you exercise regularly,
you won't keep good health.
A. unless B. whenever C. although
D. if