The correct answer is option 4: price.

Here's why:

• Perfect Competition and Price Determination:
  • In a perfectly competitive market, the interaction of overall market demand and overall market supply determines the equilibrium market price.
  • Individual firms and buyers are "price takers," meaning they must accept this market-determined price.
  • The forces of market demand and market supply set the price, and then the firms determine the quantity they will supply at that given price.