我在图书馆后面坐公车。

Wǒ zài túshūguǎn hòumian zuò gōngchē.

I get on the bus behind the library.

后面还有位子吗?

Hòumiàn hái yǒu wèizi ma?

Are there still seats in the back?

我妈妈坐在我后面。

Wǒ māma zuò zài wǒ hòumiàn.

My mother is sitting behind me.