题目

It is said that the early European playing-cards__for entertainment and education. A. were being designed      B. have designed C. have been designed      D. were designed 答案：D已知椭圆C：（a>b>0），过点(0，1)，且离心率为．(1)求椭圆C的方程；(2)A，B为椭圆C的左右顶点，直线l：x=2与x轴交于点D，点P是椭圆C上异于A，B的动点，直线AP，BP分别交直线l于E，F两点．证明：当点P在椭圆C上运动时，恒为定值．