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F1 赛车中,赛车位移与比赛时间t存在函数关系 s(t)=10t+5t2 (s的单位为m,t的单位为s).求:
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    The road in front of my school is not very wide. Every afternoon when school is over, the road becomes very crowded as children, bicycles, cars and buses fill the road. Sometimes a policeman is there to help control the traffic. However, we still have to be careful enough to stop accidents from happening.

    I am always careful when I cross the road because I ever witnessed (目击) a terrible accident. It happened just after school .As usual, the road was full of traffic. Children were running across the road to get to their cars and buses. When the traffic lights turned red, I stopped to wait, but I saw a little boy running across the road .At this moment, a car came and hit him. The boy fell and lay on the ground.  Fortunately, the car was not moving very fast and the driver successfully stopped the car before it could run over the fallen boy.

    At that time all the traffic stopped. I ran to the boy and saw some blood on the road. His head was hurt . A woman came and examined the boy. Then she lifted him and carried him to her car. They hurried to the hospital. Many people crowded around the driver who looked perplexed (糊涂的),and his face turned white. Later a policeman came and calmed the situation downAs there was nothing I could do, I left the place where the accident happened and walked down the road carefully.

    It's terrible to witness an accident. I don't think I can forget it. Certainly, I would not like to get into one. So I have to be more careful in the future.