关于运动和力的关系，下列说法中正确的是哪些（ ）
A．力是维持物体运动的原因
B．力是使物体做变速运动的原因
C．力只能改变物体运动速度的大小
D．力是改变物体运动状态的原因
A、力是改变物体运动状态的原因，维持物体运动的原因是物体的惯性，故A错误．
B、力是改变物体运动状态的原因，故力是产生加速度的原因，所以力是使物体做变速运动的原因，故B正确．
C、力是改变物体运动状态的原因，故力既能改变物体速度的大小，也能改变物体速度的方向，故C错误．
D、力是产生加速度的原因，物体的加速度不为0，物体的运动状态就会发生改变，故D正确．
故选BD．
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| However, to find out whose prayers were more powerful, they __1__ to divide the territory between them and stay on opposite sides of the island. The first thing they prayed for was__2__. The next morning, the first man saw a fruitbearing tree on his side of the island, and he was able to eat its fruit. After a week, the first man became __3__ and decided to pray for a wife. The next day, another ship was destroyed and only a woman__4__ and swam to his side of the island. But on the other side of the island, there was nothing. Soon later the first man prayed for a house, clothes and more food. The next day, like magic,__5__ of these things were given to him. However, the second man__6__ had nothing. ___7___,_the first man prayed for a ship, and in the morning he found a ship at his side of the island. The first man__8__ the ship with his wife and decided to leave the second man on the island. As the ship was about to leave, the first man heard a voice, "Why are you leaving your __9__ on the island?" "My blessings are mine alone since I was the one who prayed for them," the first man answered."His prayers were all unanswered and so he doesn't__10__anything." "You are mistaken!" the voice __11__ him. "He had only one prayer, which I answered. If not for that, you wouldn't have received any of my blessings." "Tell me," the first man asked the voice, "what did he pray for that I should__12__him anything?" "He prayed that all your prayers would be answered." | |||
| ( )1.A.continued ( )2.A.drink ( )3.A.alone ( )4.A.survived ( )5.A.some ( )6.A.even ( )7.A.Finally ( )8.A.purchased ( )9.A.relative ( )10.A.attain ( )11.A.blamed ( )12.A.offer | B．expected B．food B．sorrow B．remained B．most B．still B．Immediately B．possessed B．companion B．demand B．comforted B．pay | C．feared C．shelter C．lonely C．lived C．none C．ever C．Generally C．boarded C．colleague C．deserve C．punished C．return | D．agreed D．meal D．homesick D．struggled D．all D．instead D．Suddenly D．rented D．hero D．abandon D．abused D．owe |