题目

阅读理解 My grandparents believed that you were either honest or you were not. They had a simple saying hanging on their living-room wall: “Life is like a field of newly fallen snow. Where I choose to walk every step will show.” They didn't have to talk about it; they showed this truth by the way they lived. They understood that honesty is an inner(内部的) standard for judging your behavior. Unfortunately, honesty is in short supply today. But it is the real bottom line in every area of society and a discipline (自制能力) we must demand of ourselves. There's a story told about a如图所示，一个质量为m的物体（可视为质点）以某一速度由A点冲上倾角为30°的固定斜面，做匀减速直线运动，其加速度的大小为g，在斜面上上升的最大高度为h，则在这个过程中，物体(     )A．机械能损失了mghB．动能损失了2mghC．动能损失了D．机械能损失了