Answer:
c. is a benefit to someone other than the producer and consumer of the good.
Step-by-step explanation:
In the production process an externality is the effect of the activities not the business on the society. This can be positive or negative.
A positive externality is one in which the consumption not a produced good results in benefit to a third party other than the producer or consumer.
For example if car buyers decide to walk more often than drive it will reduce pollution in the society. This is a positive benefit to the society at large.
Or when an apple farmer plants his trees it provides nectar to the beekeeper.