----Excuse me, sir. Could you tell me________ ?

----Sorry, I don’t know.

A．where does he live

B．when will the film start

C．where is that new classmate from

D．who does the cleaning on Monday

如图所示，质量为m的小球，从A点由静止开始加速下落，加速度大小为

A．小球动能为mgh

B．小球重力势能为mgh

C．小球机械能为mgh

D．小球重力势能减少了mgh