they没复数，they的形容词性物主代词their,宾格形式是them,名词性物主代词是themselves。

pron.他们;她们;它们;用以代替he或she，指性别不详的人;(泛指)人们，人人，众人

例句：

They'll respect you as long as you play fair.

只要为人正直，别人就会尊敬你。

They are campaigning to save the area from building development.

他们正开展一场反对在这个地区进行房地产开发的运动。

Cars are checked as they come off the production line.

汽车下了生产线立即进行校验。

They agglomerated many small pieces of research into a single large study.

他们把许多小的研究课题汇集成一个大项目。