老师在黑板上写字。

Lǎoshī zài hēibǎn shàng xiězì.

The teacher is writing on the blackboard.

我们下课后要擦黑板。

Wǒmen xiàkè hòu yào cā hēibǎn.

We will wash the blackboard after class.

我以前在学校很喜欢在黑板写字。

Wǒ yǐqián zài xuéxiào hěn xǐhuān zài hēibǎn xiězì.

I used to like writing on the blackboard at school.