对于下列运动，以下说法正确的是 （ ）
A．物体运动轨迹对任何观察者来说都是不变的
B．加速度恒定的运动可能是曲线运动
C．短跑运动员最后冲刺时，速度很大，很难停下来，说明速度越大，惯性越大
D．把手中的球由静止释放后，球能竖直下落，是由于球具有惯性的缘故
答案：B
不同的观察者观察到的运动轨迹可能不同，A错。加速度恒定的运动可能是曲线运动，例如平抛运动，B对。质量是惯性大小的唯一量度，C错。球能竖直下落，是由于球受到重力作用，D错。
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| Every morning, before dropping her son off at school, my friend would stop on the way to work to grab a quick breakfast.They tended to frequent the__1__restaurant every morning grabbing an egg sandwich, juice, coffee for herself, milk for her son. One day she__2__an additional breakfast.When they had eaten a  nd walked out of the door, she stopped and said good morning to a__3__man who was sitting alone outside the restaurant and__4__ him the additional breakfast she had bought.He__5__her, grinning, telling her it was the first meal he had in a great many days.She couldn't help but feel__6__and was glad she finally took action. She told her son that she had__7__him every day that week outside the restaurant and that no one, herself included, had__8__to offer him food, drink, comfort, etc.She further__9__that homelessness can happen to anyone and the importance of service to others and__10__acts of kindness were. And so__11__her kindness tradition...each day thereafter she and her son__12__to buy and supply the homeless gentleman with breakfast.The__13__was going on until they__14__several years later but the lesson was__15__implanted (植入) in her son by then. She__16__as she told me that this kindness legacy__17__to her son, who remembered this childhood tradition and lesson.Now a college graduate and__18__employed, her son stops every day at Starbucks for his morning cup of coffee and purchases a__19__for a homeless person nearby before commuting (上下班往返) to the__20__. What a great family legacy that he can pass along to his children as well... | ||||
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