题目

双曲线的焦点到准线的距离是( )A.                                  B. C.或                         D.或 答案：解析:∵a2=9,b2=7,∴c=4.∴双曲线的焦点坐标是(±4,0),准线方程是.∴双曲线的焦点到准线的距离为和.答案:C Smith took the dictionary, ________ it and then ________ it on to Philip.          A. put away; tried        B. looked at; passed        C. paid for; put