Answer:
D. The equilibrium price of a good or service,
Explanation:
The intersection defines the best price to not only draw profit, but also to not be so expensive that the ordinary middle class person cannot afford it. Of course, the supply & demand curve entirely depends on what type of the population it is geared towards. Things that are expensive and not essential, may be expensive because it's geared towards higher-income people, who would be more likely to spend more money to obtain this luxury.