Answer:
The correct answer is: attract other firms causing a decline in the profit.
Explanation:
A monopolistic firm is a price maker. Unlike a perfectly competitive firm, it can earn positive profits in the long run. When a firm is earning profits in the long run, it attracts other firms to join the market.
When new firms enter the market it causes an increase in the supply. With a rightward shift in the supply curve, the price level declines. This causes profit to decline.