安全对策措施应具有的特点有（）。
A.隐蔽性
B.随机性
C.针对性
D.可操作性
E.经济合理性
参考答案：C, D, E
— Sally, our monitor, was late for her class this morning.
— ______? As far as I know, she never came late to class.
A．How come
B．What for
C．So what
D．Why not
试验完了信号：昼间-用检查锤由（）向车列方向作圆形转动。
A、下部
B、左
C、右
D、上部
