The correct answer is: C. gap does not exist.
A profit-maximizing firm will be in equilibrium at a point where the total revenue (TR) equals the total cost (TC). This is because at this point, the firm is making the most profit possible. If the TR is greater than the TC, then the firm can increase its profit by producing more. If the TR is less than the TC, then the firm can increase its profit by producing less. Therefore, the only point where the firm can make the most profit is at the point where the TR equals the TC.
Option A is incorrect because the gap between TR and TC can be small or large at any point. The only point where the gap does not exist is at the point of equilibrium.
Option B is incorrect because the gap between TR and TC can be small or large at any point. The only point where the gap does not exist is at the point of equilibrium.
Option D is incorrect because the gap between TR and TC does not exist at the point of equilibrium.