题目

平面内有定点A、B及动点P，设命题甲是“|PA|+|PB|是定值”，命题乙是“点P的轨迹是以A、B为焦点的椭圆”，那么甲是乙的(    ) A．充分不必要条件     B．必要不充分条件    C．充要条件           D．既不充分也不必要条件 答案：BNot only Jim but also my parents and I ______ a few places of interest since we came to China.A．has visitedB．will visitC．have visitedD．visited