Question

Which agreement rule applies to a singular collective noun functioning as a unit?

Answer 1

The answer is letter A.  
 Collective nouns could be taken as singular or plural. This depends on how each is used in a sentence. A singular collective noun is a word that functions as a single unit.
 
For example: The play’s cast is currently rehearsing. The word “cast” is a singular subject. Although there are many members of the cast, they still function as one unit.

The plural collective noun on the other hand indicates many units and thus takes a plural verb. 

Answer 2

the answer is A because i got it right on my quiz