问题
选择题
There are many trees on ____ sides of the river. [ ]
A. any
B. either
C. both
D. neither
答案
答案：C
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There are many trees on ____ sides of the river. [ ]
A. any
B. either
C. both
D. neither
答案：C
，在BC段加速度恒为
，两者方向相同。若有
，则
