Answer :
It's definitely A.
Eg : Police is an institution. The police come (police members, not the entire police) when bad things happen.
The correct answer is A. use a singular verb.
If a noun is singular, but also collective, it means that it has the form of a singular noun, but refers to more than one entity. However, based on the context, it will either take a singular, or a plural verb.
For example: The team is quite good (where the team is a collective noun referring to all members together) VS. The team are not behaving properly (where this refers to all members individually).