In a perfectly competitive market, how is the market equilibrium determined in the short run? In a perfectly competitive market in short-run equilibrium, ________. A. only demand determines the price and quantity bought and sold in the market because all firms are price takers B. only supply determines the price and quantity bought and sold in the market because the good has many substitutes C. market supply and market demand determine the price and quantity bought and sold in the market D. the price and quantity bought and sold in the market are determined by the shutdown point