The correct answer is option 4: price.

In a perfectly competitive market, no single buyer or seller has the power to influence the market. Instead, the market price is primarily determined by the interaction of total market demand and total market supply.

• Market Demand represents the total quantity consumers are willing to buy at different prices.
• Market Supply represents the total quantity firms are willing to sell at different prices.

The point where market demand and market supply intersect determines the equilibrium price. In perfect competition, individual firms are known as price takers because they must accept the market price determined by these market forces.

Other Options:

• Demand and Supply (Options 1 & 2): These are the determining forces themselves, not what is primarily determined by them.
• Quantity (Option 3): Equilibrium quantity is also determined at the intersection of demand and supply. However, the primary feature emphasized under perfect competition is that market price is determined by these market forces and firms have no control over it.