题目

The governments are very_______ about setting a new policy and make no decision until they are quite sure it is the right one. A． particular             B． concerned C． cautious              D． certain 答案：C过椭圆Γ：＝1(a＞b＞0)右焦点F2的直线交椭圆于A，B两点，F1为其左焦点，已知△AF1B的周长为8，椭圆的离心率为.(1)求椭圆Γ的方程；(2)是否存在圆心在原点的圆，使得该圆的任意一条切线与椭圆Γ恒有两个交点P，Q，且⊥？若存在，求出该圆的方程；若不存在，请说明理由．