Remember to use a plural verb with a plural subject and a singular verb with a singular subject. This may sound obvious, but there are several reasons why it may become less straightforward:
• Some words look as though they are singular when they are in fact plural, especially words ending in -a like criteria, bacteria and phenomena. The singular forms for these are criterion, bacterium and phenomenon.
Use plural verbs.
• The bacteria multiply rapidly. --- This is right sentence.
• The bacteria multiplies rapidly. --- This is wrong sentence.
• These are important criteria. --- This is right sentence.
• This is an important criteria. --- This is wrong sentence.
• In Latin, data and media are plural nouns. In English they used to be treated as plurals and took a plural verb. Now, however, unless you are writing in a formal scientific context you should regard them as normal singular nouns that go with a singular verb.
• Collective nouns (e.g. crew, team, government, committee) can be treated as either singular or plural. As a general rule, it is best to use a plural form when emphasizing the separate members of the group.
• The committee were arguing about the finances.
And a singular form when treating the group as a whole.
• The committee is delighted to offer you the prize.