社会治安防控体系建设评估中只有总评分低于60分的，才定为不达标
参考答案：错
The boy was led _______while crossing the road.[ ]
A .in the hand
B. by his hand
C. by hand
D. by the hand
对低频信号发生器的输出电压幅度有什么要求为什么
