We can't listen to music in the class.我们不能在上课时听音乐.
We mustn't be late for school.我们不应该上学迟到.
We had better not make noisy in classroom.我们最好不要在教室里制造噪音.
It's necessary for us to listen to the teacher carefully.上课认真听讲对于我们来说是必要的.
It's our duty to finish our homework.完成家庭作业是我们的职责.