题目

I have a friends who lives by a three-word philosophy: Seize the moment. Just possibly, she may be the wisest woman on this planet. Too many people put off something that brings them joy just because they haven't thought about it. Don't have it on their schedule, and didn't know it was coming or they are too strict to depart from their routine. I can't count the times I called my sister and said, “How about going to lunch in half an hour?” She would gasp and stammer(结结巴巴地说), “I can't. I have clothes on the line. My hair is dirty. I wish I had known it yesterday, I had a 若一个椭圆长轴的长度、短轴的长度和焦距成等差数列，则该椭圆的离心率是     A．   B．   C．   D．