Answer:
A) auction off a limited number of sheep-grazing permits.
Step-by-step explanation:
The phrase tragedy of the commons is used to exemplify a situation where individuals act upon their self interest and contrary to the common good.
In this case the sheep herders are acting selfishly because they are destroying the communities' ecological resources (grazing resources are pasture). In order to prevent this, the town government should auction a limited number of sheep grazing permits. That way the number of sheep can be kept under control and at a reasonable amount that doesn't destroy the town's ecological resources.