题干
Mary and Lily are good friends，and they love to sit by the seaside，________to each other for hours.
A：talking
B：to talk
C：having talked
D：to have talked
答案(点此获取答案解析）
A
右支上一点，
，分别是双曲线的左、右焦点，I为
的内心，若 
成立，则双曲线的离心率为（ ）