Answer:
d. benefits that accrue to those who don't pay.
Step-by-step explanation:
Free rider is a form of market failure where benefits accrue to those who don't pay for a good or service. The free rider problem leads to an inefficient allocation of resources.
For example, a well that would benefit all the members of a rural community is been built. Members of the community are encouraged to donate to this project. All donate except Donald. Despite Donald not donating, he still uses the well. Donald is free riding.
I hope my answer helps you.