题目

- Could you tell me                    - You' d better keep a diary in English as often as possible.          A. when I can improve my written English          B. how I can improve my written English          C. if can I improve my written English 答案：B已知椭圆C的中心在坐标原点，焦点在x轴上，椭圆C上的点到焦点距离的最大值为3，最小值为1。 （1）求椭圆C的标准方程； （2）若直线l：y=kx+m与椭圆C相交于A，B两点（A，B不是左右顶点），且以AB 为直径的圆过椭圆C的右顶点，求证：直线l过定点，并求出该定点的坐标。