题目

(An excerpt from ＜Jack’s Endless Summer＞)Then one evening, Jack is sitting in his room looking out of the window. Jim is sitting on the bed playing with his rocket. It is a cool evening at last. A light wind is blowing. Summer is finally coming to an end.It is a quiet evening, too. For once, nobody is playing loud music. Jack can only hear the distant sound of the traffic on the ring road around Westbourne.Suddenly there is a noise in the back garden. Nemo jumps onto the fence, looks up at the sky, and meows.“What is he looking at?” thinks Jack.And then he hears a distant cry. A stra直线y＝x＋1截抛物线y2＝2px所得弦长为2，此抛物线方程为(　　) A．y2＝2x                             B．y2＝6x C．y2＝－2x或y2＝6x                  D．以上都不对