题目

Sandy didn’t tell her parents that she was going home because she wanted to give them a _______.     A. gift      B. call     C. surprise      D. note   答案：C已知抛物线y2=6x，过点P（4，1）引一条弦P1P2使它恰好被点P平分，求这条弦所在的直线方程及|P1P2|．