The correct answer is: A. Equal to; average total cost is minimized.
Marginal cost is the cost of producing one additional unit of a good or service. Average variable cost is the total variable cost divided by the number of units produced. Average total cost is the total cost divided by the number of units produced.
When marginal cost is equal to average variable cost, average total cost is minimized. This is because the additional cost of producing one more unit is equal to the average cost of producing all the units that have already been produced. This means that the company is producing at the most efficient level.
Option B is incorrect because when marginal cost is less than average variable cost, the company is producing at a loss. This is because the company is spending more money to produce each additional unit than it is making from selling that unit.
Option C is incorrect because when marginal cost is greater than average variable cost, the company is making a profit. This is because the company is making more money from selling each additional unit than it is spending to produce that unit.
Option D is incorrect because average variable cost is minimized when marginal cost is equal to average variable cost.