你读一下the freedictionary 在each词条下的用法说明。即each用在动词之后时，代词用单数或复数都是可以的。

Usage Note: In standard usage, the subject of a sentence beginning with each is grammatically singular, and so the verb and following pronouns must be singular: Each of the apartments has (not have) its (not their) own private entrance (not entrances). When each follows a plural subject, however, the verb and subsequent pronouns remain plural: The apartments each have their own private entrances (not has its own private entrance). When each follows the verb, it has been traditionally considered acceptable to say either The boys have each their own bike or The boys have each his own bike, though both of these (and especially the latter) are likely to seem stilted in comparison to The boys each have their own bike or The boys each have their own bikes.