题目

Once a circle missed a wedge (楔子). The circle wanted to be whole, so it went around looking for its missing piece. But because it was incomplete and therefore could roll only very slowly, it admired the flowers along the way. It chatted with worms. It enjoyed the sunshine. Finally it found a piece that fit perfectly. It was so happy. Now that it was a perfect circle, it could roll very fast, too fast to notice flowers or talk to the worms. When it realized how different the world seemed when it rolled so quickly, it stopped, left its found piece by the side of the road and rolled slowly aw设m、n都是不大于6的自然数，则方程C6mx2-C6ny2=1表示双曲线的个数是（ ）A．6B．12C．16D．15