What must a firm have to maintain a monopoly?

Question

Quizplus · Accepted Answer

To maintain a monopoly, a firm must have an insurmountable barrier to entry, which prevents other firms from entering the market and competing with them. Without this barrier, new firms would enter and the monopoly would be quickly eroded. Perfectly inelastic demand and marginal revenue equal to demand may increase the monopoly's power, but they are not necessary for it to exist. Having few competitors can also help a firm maintain market power, but it alone does not guarantee a monopoly.

What Must a Firm Have to Maintain a Monopoly