If a profit-maximizing, competitive firm is producing a quantity at which marginal cost is between average variable cost and average total cost, it

a. keep producing in the short run but exit the market in the long run.
b. shut down in the short run but return to production in the long run.
c. shut down in the short run and exit the market in the long run.
d. keep producing both in the short run and in the long run.

a. keep producing in the short run but exit the market in the long run.

Explanation:

To answer the question, there is a need to look at the effect of the situation on the firm both in the short- run and the long-run

Short Run Effect

The Marginal cost is between average variable cost and average total cost. The business can still continue producing goods because the quantity being produced is still able to cover the average variable cost. This means that the firm is still able meet its variable costs by setting the price of its goods to its marginal cost which is an amount greater than its average variable cost.  

Long Run Effect

However, in the long-run the company will begin to have issues even meeting other important costs such as the fixed costs associated with production and as such, the firm will need to exit the market in the long run. For instance the cost of long term loans (principal and interest) may not be covered by the net income of the firm.