—May I swim in the river, Mum? — . [ ] A

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问题选择题

— May I swim in the river, Mum?

— . [ ]

A. No, you aren't

B. Why do you ask me

C. No, you can't

D. I can't go with you

答案

答案：C

选择题

__________ his work was still as it had been?

A．It was why that

B．Why is that

C．It is why that

D．Why was it that

实验题

如图所示，是某同学研究牛顿第一定律的模拟实验装置．在水平桌面上铺上粗糙程度不同的材料（如毛巾、棉布、木板等），让小车自斜面顶端从静止开始滑下，三次实验现象如下，比较小车沿水平面运动的距离。

（1）三次实验中，让小车自斜面顶端从静止开始滑下，使小车运动到斜面底端时的速度。

（2）三次实验中，小车在表面上滑得最远，但最后会停下来，这是因为________阻力改变了它的运动状态。

（3）进一步推理可知，若水平面绝对光滑，则车会在水平面上做运动。可见，力不是使物体运动的原因，力是改变物体___________的原因。