Are you confused with collective nouns? This article discusses the proper usage of singular and plural collectives.
British and American style guides tend to agree that collective nouns like audience, committee, and data can be construed as either singular or plural, according to whether the word is perceived as a unit or as individual items. As it says in The Chicago Manual of Style, “a singular verb emphasizes the group; a plural verb emphasizes the individual members.” Plural collectives can also be identified by pronouns used with them. Learn more.