上紧发条的玩具车在水平桌面上由静止开始运动所需的能量来源于（ ）
A．重力势能
B．电能
C．弹性势能
D．动能
答案：C
题目分析：本题主要考查动能和势能的相互转换。玩具车在水平桌面上运动，高度不变，质量不变，故重力势能不变。上紧发条的玩具车，此时发条的弹性形变量最大，弹性形变越大，弹性势能越大。车由静止开始运动，弹性势能减小，转换成了车的动能。故选项C。
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| We have a big playground in our school. We all like to 1 games 2 after school. It's Friday. We have only two classes 3 the afternoon. When school is 4 , a lot of students go to the playground. Look! The boy of Grade Two are 5 a basketball match. Some girls are 6 and shouting ( 大叫 ). Football is our favorite sport. Many teachers are also 7 football. Li Ming, Li Lei and Wei Fang are students of Grade One. They are 8 volleyball. They are playing very 9 . It's half past five now. It's time 10 home. The students all leave the playground. | |||||
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