What does having a long run equilibrium indicate about a society a. society’s supply and demand have stagnated b. society is using all of its resources efficiently c. society’s needs are being fully met d. society is not using all of its resources effectively

the answer is b. society is using all of its resources efficiently 
A market will reach the state of equilibrium if the amount of products being supplied match the amount of demands in the mareket.
This indicates that there will no abundance/leftovers product lying around in the market, and this mean that the society has been using their resources efficiently.

Long run equilibrium indicates that a society's using it's resources usefully. If something has stagnated it means that something has stayed the same with no major fluctuations. Equilibrium means that there is a balance between two forces, in this case the society and it's resources.