基准本身正好等于一个计量单位。( )
参考答案：错
解析：[正确] 基准本身并不一定正好等于一个计量单位。)
In the dark street, there wasn't a single person ____ we could turn for help. [ ]
A. that
B. who
C. from whom
D. to whom
如图所示，一轻杆两端固定两个小球A、B，mA=4mB，跨过定滑轮连接A、B的轻绳长为L，求平衡时OA、OB分别为多长？
