题目

 Mary asked me, “Have you really realized the part the computer has in the daily life?”  A. made              B. given   C. caused                  D. played 答案：D已知椭圆C:  (a>b>0)的两个焦点和短轴的两个端点都在圆上.(I)求椭圆C的方程；(II)若斜率为k的直线过点M(2,0),且与椭圆C相交于A, B两点.试探讨k为何值时,三角形OAB为直角三角形.