题目

______ the Internet is of great help, I don’t think it’s a good idea to spend too much time on it.A. If             B. Bacause      C. While        D. As 答案：C已知双曲线的标准方程为，F为其右焦点，A1，A2是实轴的两端点，设P为双曲线上不同于A1，A2的任意一点，直线A1P，A2P与直线x=a分别交于两点M，N，若，则a的值为（ ）A．B．C．D．