汽车遇情况紧急刹车，经3s停止，刹车距离为9m．若汽车刹车后做匀减速直线运动则汽车停止前最后1s的位移大小是（　　）

A．4m

B．3m

C．2m

D．1m

Whenever your marine radio is on，FCC Rules require you to monitor（）.

A.a commercial ship-to-ship channel

B.the last frequency that was used

C.the distress and calling frequency

D.the radio only if expecting a call