题目

The teacher told me that the students I wanted to see were seen___ football on the playground just now.    A.playing     B.to be playing    C.play        D.to play 答案：A过双曲线的一个焦点作垂直于实轴的弦， 是另一焦点，若是钝角三角形，则双曲线的离心率范围是（    ）A．B．C．D．