(2013·江西六所重点高中一模)We ________ take clean drinking water for granted. One day we may run out of it.

A．needn't

B．can't

C．won't

D．shouldn't

自动闭塞区段，机车信号显示一个半黄半红色闪光灯光，表示列车接近的进站或接车进路信号机开放（）信号或通过信号机显示容许信号。