Answer:
The correct answer is letter "C": the sum of private and external costs.
Step-by-step explanation:
Neoclassical economics -based on supply and demand as market drivers- define the social costs of transactions as the sum of private costs inherent in the operation and the costs consumers set because of being exposed to the transaction or the external costs. This cost differs from the private costs which are the expenditures a producer incurs in the production of a good or service.