Answer:
The correct answer is option a.
Explanation:
In a competitive market, there is no limitation on entry and exit, entry and exit are free. The firms in a perfectly competitive market are price takers. They have a horizontal line demand curve which also represents average revenue and marginal revenue.
The firms will enter the market in the long run if the price or marginal revenue is greater than average total cost. The firms will be maximizing their profits if the average total cost is equal to marginal revenue and price.
The firms will exit the industry if price and marginal revenue fall below the average total cost.
