You won't pass the exam _____ you study hard. [ ]
A. if
B. when
C. after
D. unless
答案:D
如果∠α和∠β互为补角,并且∠β的一半比∠α小30°,求∠α和∠β的度数.
On receiving a phone call from his wife _____ she had a fall, Mr. Gordon immediately rushed home from office. [ ]
A. says
B. said
C. saying
D. to say