题目

We have twenty minutes’ rest between classes. Look! Most of us are playing during the rest time. Some students are on the playground. They are having a basketball game. Oh! A boy is running with a ball. And another is trying to stop him. They are so cool. And there are some girls watching the game. Some students are in the classroom. They are talking. A few of them are reading or doing homework. Look! A girl is looking at the birds in a tree in front of the classroom. She must be thinking of something interesting because she is smiling.What are the teachers doing? Do you know? Some of them a若m＜n，则下列各式中错误的是（　　）A．m-3＜n-3B．5m＞5nC．-m3＞-n3D．-m＜-n