------ He should have been warned of the danger.

------_________, but he wouldn’t listen to me.

A．So he was

B．So was he

C．So should he

D．So he should

64D半自动闭塞，只有在区间空闲时，由发车站发出请求发车信号，并收到接车站的同意接车信号之后，发车站的（）才能开通，出站信号机才能开放。

A.联锁设备

B.列车进路

C.闭塞机

D.信号按钮