Answer:
the price elasticity of demand for the firm's output
Step-by-step explanation:
A monopoly is a single firm operating an industry.
The degree to which monopolies can mark up prices depends on the price elasticity of demand of consumers.
Price elasticity of demand measures the rate at which quantity demanded changes when price changes.
If the demand for the product of a monopoly firm is inelastic, firms can mark up their prices to any degree in the absence of government regulation.
If the demand for the product of a monopoly firm is elastic, it limits the degree to which the firm can mark up prices because if price is increased to a certain level, quantity demanded falls.