Answer:
A
Step-by-step explanation:
A free rider is a person who benefits from a good or service (in this case, coffee) without paying it. In most cases, free riders benefit from public goods and coffee is, in some way, a public good in the office because everybody who works there can have a cup of it.
Other people in the office is not a free rider because they toss change when they pour a cup of coffee, then they are contributing their fair share.