Answer: a. the free-rider problem
Step-by-step explanation:
The free-rider problem is a situation described as market failure that occurs when public goods, services or resources are benefited by those who do not contribute or contributes little towards its availability. It is a problem because those who did not pay for the good or service might keep having access to it. The problem might also lead to economic failure of not been able to produce or make such goods or services available.