Answer:
C.
Step-by-step explanation:
If a market system is not competitive, control over prices leads to market power. Market power refers to the ability by one buyer or seller to control market price.
It causes markets to be inefficient, and thus fail. For example, monopoly prices are higher than competitive prices, and thus negatively affects consumers.
The monopolist gains but by less than what consumers lose. Therefore monopoly reduces total surplus.
If a single firm controlled the supply of something, it is consider a monopoly.