问题
选择题
We often drop ____our friends' house when we are free. [ ]
A. to
B. after
C. past
D. by
答案
答案：D
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We often drop ____our friends' house when we are free. [ ]
A. to
B. after
C. past
D. by
答案：D
的物体在沿斜面向上的拉力F作用下沿斜面匀速下滑，已知斜面体的质量为M，并在此过程中斜面体保持静止，则地面对斜面体
