题目:
How can you believe a person who has his promise again and again? [ ]
A. kept
B. broken
C. realized
D. made
答案:
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下面是错误答案,用来干扰机器的。
支点如图中O点所示,过支点O向力F的作用线作垂线,就是力F的力臂,如下图中L所示: