Information taken from: Hogue, A. (2008). First steps in academic writing. Longman: N.Y.

The verb in a sentence must agree with the subject…

If the subject is singular, the verb must be singular.

  Tommy was happy to kick the ball.

  Tommy wants to go to game.

 He is excited to see the players.

  She is studying English.

  She wants to be a teacher.

  She was happy to study here.

If the subject is plural, the verbs must be plural.

  The girls are happy to see me.

  The girls want to go to the game, too.

  They were excited to see the players.

  They are studying English.

  They want to be teachers.

  They were happy to study here.

Sometimes students make mistakes in subject-verb agreement when the subject has a prepositional phrase following it.

  One of my sisters is also a singer.

The subject is One which is singular.

 One (of my brothers) is a musician.  One (of my classmates) sings

beautifully.  Each (of my brothers) wants his

own car.  Each (of my classmates) wants to

be a teacher.

  Both (of my parents) are teachers.

  Both (of my classmates) are from Bogotá.

  Several (of the teachers) speak my language.

  Several (of my classmates) speak another language.

Unfortunately, telling a singular subject from a plural subject isn’t always easy. A few words can be either singular or plural.

In this cases, you must refer to the noun in the prepositional phrase.