Prices ______ all the time. It's no wonder that we've spent so much money recently.

A．rose

B．had risen

C．were rising

D．have been rising

火星有两颗卫星，分别是火卫I和火卫II，它们的轨道近似为圆，已知火卫I的周期为7小时39分，火卫II的周期为30小时18分，则两颗卫星相比[ ]

A．火卫II距火星表面较近

B．火卫II的角速度大

C．火卫I的运动速度较大

D．火卫I的向心加速度较小