Mr Green stood up in defence of the 16yearold boy, saying that he was not the one________. [ ]

A. blamed  

B. blaming

C. to blame  

D. to be blamed

如图所示，空间中存在竖直向上的匀强电场，一个质量为m的小球沿虚线作直线运动，轨迹上A、B两点的竖直高度差为H，重力加速度为g，则在小球从B到A的过程中

A.电场力对小球做功－mgH

B.小球的动能保持不变

C.小球的机械能增加mgH

D.小球的重力势能和电势能的和增加mgH