题目

Recently Peter________to do his homework, and instead insists on wasting his time playing com-puter games, which extremely annoys his father. A. had been refusing      B. has been refusing  C. was refusing  D. refused 答案：B已知双曲线中心在原点, 两条渐近线的方程是y＝±x, 双曲线过点 M(,-1), 那么两准线间的距离是[    ]A.　　　　B.C.　　    D.