When entry barriers into a market are high :. i. a monopolist will always be able to make an economic profit.
b. rival firms will enter and drive price down to the level of per-unit costs if the firms in the market are making economic profit.
c. entry into the market will not take place, at least not quickly, even if the firms currently in the market are making economic profits.
d. the producers in the market will have little or no incentive to produce efficiently (at a low cost).