题目

Read and choose. 读短文，根据上下文选择正确的选项完成句子。When you are in England, you must be very careful in the streets 1 the traffic drives on the left. When you cross a street, you must look to the 2 first and then left. In the morning and in the evening when people go to or come from work, the streets are very 3 . Traffic is the most dangerous(危险的)then. When you go by bus in England, you have to be 4 , too. Always remember the traffic moves on the left. So you must be careful. Have a look first, 5 you will go the wrong way. （1） A . so B . 如图①，抛物线y=ax2+bx+c与x轴相交于O、A两点直线y=-x+3与y轴交于B点，与该抛物线交于A，D两点，已知点D横坐标为-1．（1）求这条抛物线的解析式；（2）如图①，在线段OA上有一动点H（不与O、A重合），过H作x轴的垂线分别交AB于P点，交抛物线于Q点，若x轴把△POQ分成两部分的面积之比为1：2，请求出H点的坐标；（3）如图②，在抛物线上是否存在点C，使△ABC为直角三角形？若存在，求出点C的坐标；若不存在，请说明理由．