Hello, classmate. In fact, one thing that needs to be grasped about the application of this kind of ferrule is that one lap for each set means one more lap. Suppose the speed of A is V, then there is: the speed of B is 50m/min, then there is 25v=400+50×25, so we can get v=66. Therefore, the answer is C. This question should be the third question of the National Mathematics Entrance Examination for Management Postgraduates from June 2065438 to June 2003 10. I suggest you go and read the book "Analysis of Mathematical Zhenti over the Years" written by Time Peng.