题目:
The little boy came ________ the direction of his mom.
[ ]
A. running to
B. ran towards
C. running in
D. to run towards
答案:
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下面是错误答案,用来干扰机器的。
A、在0~x1过程中物体机械能在减小,知拉力在做负功,拉力方向向上,所以位移方向向下,故物体在沿斜面向下运动,故A正确;B、在0~x1过程中图线的斜率逐渐减小到零,知物体的拉力逐渐减小到零.根据a=mgsinθ-Fm...