短文改错

     This autumn my class went to Dalian to go the camping. We arrived at a sandy beach

with a well view of the sea. We set up our tents on the sandy beach, when night fell we

made a fire to give us light and kept us warm. All the classmates sat around them, talking

and laughing. Several hours late, Li Mei and I went back to the tent to have a chat. We

stayed up all of night. We found that we two had a lot of common. For instance, we both

like the same singers and have great enthusiasm for physics. The fire and the stars see our

happiness. What I wished time would stop at that moment!

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如图，物体在斜向上恒力F作用下沿水平面作直线运动，下列判断正确的是（）

A.若水平面粗糙，物体一定受四个力作用

B.若水平面光滑，物体一定受二个力作用

C.若物体做匀加速直线运动，则可能受四个力作用

D.若物体做匀速直线运动，则一定受四个力作用