My brother Tom was very selfish when he was a little boy.He did not want share things with other people. For example, when he bought a chocolate cake he put them in a secret place where I couldn’t find . Then he ate it all by himself. He never helped other. He said he is busy . That is, a game of tennis making him very busy. He did not care if something he did made people angry. For instance, on one night he played strong and loudly music till four o’clock on the morning. But he is difference now. He often helps grandma with housework, helps his classmates with their lessons.

3吨矿车轮缘磨损余厚不小于13毫米，踏面磨损余厚不小于（）毫米。

A、7

B、8

C、9

D、10