题目

质量为m的小球从高h处由静止开始自由下落，以地面作为零势能面。当小球的动能和重力势能相等时，重力的瞬时功率为 A．             B．               C．            D． 答案：B---Don't you think it______ of some teenagers to be crazy about pop stars?---Well, I don't think so. We were once young and had the similar experiences.A. creative B. sillyC. wise D. curious