题目

    One day, Wilson was walking quietly along the road when someone hit him hard on the back of his neck. He looked behind him, and saw a young man whom he had never seen before.    “How dare you hit me like that?” shouted Wilson.    The young man said he had mistaken Wilson for a friend of his and that he thought Wilson was making a lot of noise about nothing.    This insult (侮辱) made Wilson even angrier, of course, and he at once decided to bring the young man before a judge.    Now, the judge, who heard the case was a friend of the young man's father's, and, although 两条平行线l1：3x+4y-2=0，l2：ax+6y=5的距离等于（　　）A．35B．75C．715D．415