Answer: When a perfectly competitive firm finds that its market price is below its minimum average variable cost, it will sell D. nothing at all; the firm shuts down.
Explanation: A perfectly competitive firm does not exist because it a theoretical market structure where all firms sell the same product, they are price takers, the market has no influence on price and there is full freedom. If the market price is below what it will cost to produce the products, the firms will stop producing their products and shut down.