如图所示，一半径为R、质量为M的1/4光滑圆弧槽D，放在光滑的水平面上，有一质量为m的小球由A点静止释放，在球沿圆弧下滑到B点的过程中，下述说法正确的是（）

题干

A：小球的机械能守恒

B：小球和槽组成的系统机械能守恒

C：小球、槽和地球组成的系统机械能守恒

D：小球、槽和地球组成的系统机械能不守恒

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C

Ways to spend holidays
Families	Places to go	Things to do
Mario's	France	They____to many places there．
Jack's	____	They went to ____there．
David's	Shanghai	They visited ____there．
Tom's	The mountains	Tom asked his children to see them and ____on them．