他上课的时候常常睡觉。

Tā shàngkè de shíhou chángcháng shuìjiào.

He frequently sleeps in class.

今天上午我们有三节课。

Jīntiān shàngwǔ wǒmen yǒu sān jié kè.

We have three classes this morning.

上课的时候不要玩手机。

Shàngkè de shíhou búyào wán shǒujī.

Don’t play with your phone during class.