题目

Although the old lady has a daughter and two sons ,______ live with her．       A．none of whom                  B．neither of them       C．all of whom                    D．none of them 答案：D 解析: 略已知椭圆的左、右两个焦点分别为、，若经过的直线与椭圆相交于、两点，则△的周长等于        .