Answer:
b) one firm has the exclusive ownership of a necessary resource
Step-by-step explanation:
A monopoly is a situation where a single supplier of a commodity.
This gives the supplier the benefit of fixing a price that maximises profit for them. Consumers have no alternative so they pay the high price for the commodity.
There is no substitute good so there is no competition from other firms. Price is usually set at a high level so that the monopoly enjoys profit high above its marginal cost.
Monopolies exist because one firm has the exclusive ownership of a necessary resource not available to other firms.