复数代词they, them, their 可以表示单数意义吗

在通常情况下，复数代词they, them, their 表示复数意义。如：

As is usual with children, they soon got tired. 孩子们一贯如此, 他们很快就厌倦了。

Although they are twins, they look entirely different. 他们虽是孪生，但是相貌却完全不同。

If the trees had been given more attention, they could be grown better. 要是对这些树多加注意，它们会长得更好些。

When guests leave the host usually sees them out. 客人走时，主人通常送出门。

We invited 12, but only a handful of them came. 我们邀请12人，但只有几个人来。

The Irish are very proud of their sense of humour. 爱尔兰人为自己的幽默感而自豪。

Most of the families have modernized their kitchens. 大多数家庭已实现厨房设备现代化。

但是，在实际运用中，有时也可以用复数代词they, them, their来指代性别不明的单个人（即单数）。如：

Everyone knows what they have to do, don’t they? 每个人都知道自己必须做什么，对吗？

If either David or Janet come, they will want a drink. 大卫或珍妮特来的话，是会要喝酒的。

If any of them comes to see me, let them wait for me to come back. 如果他们中有人来看我，请叫他们等我回来。

When a person gets married, they have to start thinking about their responsibilities. 一个人结了婚，他们就得考虑考虑自己的责任。