When changing lanes, a driver should use his   turning signal to let other drivers know  ____   .   [ ]

A. he is entering which lane  

B. which lane he is entering    

C. is he entering which lane  

D. which lane is he entering

路侧护栏能防止失控车辆冲出路外，碰撞路边障碍物或其他设施，它的设置主要以路侧事故严重度为依据，路侧护栏最小设置长度为( )m。

A．50

B．60

C．70

D．80