题目

A well-known speaker started his talking by holding up a $20 bill. In the room of 200, he asked, Who would like this $20 bill? Hands started going up. He said, I am going to give this $20 to one of you, but first, let me do this. He began to crumple(弄皱) the 20 dollar note up. He then  asked, Who still wants it? Still the hands were up in the air. Well, he replied, what if I do this? He dropped it on the ground and started to grind it into the floor with his shoe. He picked it up, now crumpled and dirty. Now, who still wants it? Still the hands went into the air. My friends, you have all l不定项选择如图所示，一个物体由静止开始，从A点出发，分别经三个倾角不同的光滑斜面下滑到同一水平面上的C1、C2、C3处，则下列说法正确的是A．三个过程中，所经历的时间都相等 B．在C1、C2、C3处的动能相等C．三个过程中，动量的变化大小相等D．在C1、C2、C3处的动量相同