The correct answer is D.
Collective nouns denote a group of people, animals or objects. They are words for single things that are made up of more than one person, animal or object.
Some examples of collective nouns are: class, herd, jury, team, group, audience.
In the example above, the word class is a collective noun because it refers to a number of students. The use of the verb is singular because the word class denotes the group as a whole, even if it's made up of various individuals.
