Answer:
The correct answer is: enter the market; exit the market.
Explanation:
In a perfectly competitive market, there is no restriction on entry and exit of firms. So profits will attract other potential firms to join the market. And when the existing firm incurs losses it will cause them to stop operating and exit the market.
Because of this, the firms in competitive settings are motivated to produce at a low cost and they come up with new ideas to please customers so that they earn a profit.