everyone knows these things,don't they?
陈述部分的主语是 everybody, everyone, anybody, anyone, somebody, someone, nobody, no one, none, neither 时, 其反意疑问句的主语需用复数代词they.例如：
Everyone is here, aren't they? 大家都到了,是吗?
No one knows about it, do they? 没有人知道这件事,对吗?