题目

Ladies and gentlemen, due to an unexpected accident, one of the singers whom all of you ________ to see won't be performing tonight. A . are coming B . have come C . come D . came 答案：B过双曲线的一个焦点引它到渐进线的垂线，垂足为，延长交轴于，若，则该双曲线离心率为（    ） A．        B．        C．           D．3