It took the police a long time to find some evidence. The new evidence led to _______.

A．the robber having caught

B．catch the robber

C．the robber being caught

D．the robber to be caught

如图3-6-9所示，光滑导轨水平放置，匀强磁场竖直向上，金属棒ab、cd质量相等.开始给ab一个冲量，使它具有向右的初速度v，经过一段时间后，金属棒cd的速度(    )

图 3-6-9

A．向右，等于v

B．向左，等于v

C．向右，等于v/2

D．静止不动