找考题网-背景图
单项选择题

You are approaching a vertical lift bridge.You know the……

You are approaching a vertical lift bridge.You know the span is fully open when().

A.Three white lights in a vertical line are lit
B.A red light starts to flash at about 60 times a minute
C.A yellow light is illuminated on the bridge pier
D.There is a range of green lights under the lift span