The basics of subject-verb agreement. The number of the subject determines the number of the verb. In other words, if the subject is plural, the verb, too, must be appropriate for plural subjects. The following samples demonstrate singular and subject verbs.
It has been said that a monkey, randomly typing away on a typewriter (in the days when typewriters replaced the pen or plume as the preferred instrument of writing) could re-create Shakespeare-- but only if it lived long enough (this is known as the infinite monkey theorem).