The rules of using this perfect are slightly different in British and American English. Researchers have also found that among English American writers, individual preferences sometimes determine whether the simple past or the current perfect is used. That is, an American English writer can choose the simple past in a place where another American English writer can choose the perfect present. This composite subject therefore requires a singular verb to agree. A clause that begins with whom, what or what and between the subject and the verb can create problems of correspondence. In general, each sentence describing a completed action should contain a verb in the past tense. However, a prepositional sentence inserted between the subject and the verb sometimes complicates the agreement. Perfect present: Use the present perfectly to display an action that took place at a non-specific time in the past. This action is relevant in the present. The Perfect present is sometimes used to introduce background information into a paragraph. After the first sentence, the form of time moves to the simple past. But if the subject is plural, then the verb must be plural.
The subject-verb compliance rules apply to all personnel pronouns except I and U which, although SINGULAR, require plural forms of verbs. .