"Have you _____ him to give up smoking?""No. I _____, but he wouldn't listen."
A. persuaded/tried
B. tried/persuaded
C. tried/tried
D. persuaded/persuaded
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I ______ see you, but I didn't, for I had no time.
A. had wanted to
B. has wanted to
C. wanted
D. was wanted
She ______ the door before she goes away.
A. had locked
B. is locking
C. has locked.
D. was locking.
解析法求解平面汇交力系的平衡问题，需要对力求投影。
A. 对
B. 错
如果一个力在某轴上的正交分力与坐标轴的指向相同，那么这个力在该轴的投影就为正。
A. 对
B. 错
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