汽车下坡制动无效时，应利用紧急停车车道和一切有利于减速的障碍物或空阔场地进行减速停车。
参考答案：对
机房内钢丝绳与楼板孔每边间隙均为（）mm。
A、5~10
B、10~15
C、20~40
D、40~60
It was not until dark _______ he found _______ he thought was the correct way to solve the problem.
A．that; what
B．that; that
C．when; what
D．when; that
