实验器材：1cm厚的石膏板若干，质量为50g的鸡蛋数枚。

实验过程：无风环境下，将鸡蛋从楼上静止释放，砸中铺在草坪上的石膏板，记录实验现象。

    There is a woman ____（name）Daisy who has devoted all her life to ____（attend）to the homeless children. It's generally recognized that what she has done for children ____（deserve）to be respected by everyone. ____（personal）speaking, her selfless behavior sets a good example to us.

    There was a time when I came across Daisy who ____（invite）to deliver a speech, during which she indicated, “____（take）care of homeless children is just ____ ordinary job, but it doesn't mean that you can look down ____it. Every job is equal. We can't say which one is ____（good ）.” She also said, “Once you set out to do something, you ought to carry on with it to the end, ____ you will gain nothing in the end.”

如图所示，两根和水平方向成α角的光滑平行的金属轨道，上端接有可变电阻R，下端足够长，空间垂直于轨道平面的匀强磁场，磁感应强度为B，一质量为m的金属杆从轨道上由静止滑下，经过足够长时间后，金属杆的速度会达到最大值v_m，则（   ）