Answer:
D. Market supply and market demand determine the price and quantity bought and sold in the market.
Step-by-step explanation:
In perfectly competitive market, equilibrium price and quantity is determined at the point where the aggregate supply curve and aggregate demand curve intersect.
If either supply or demand changes, the supply/demand curve will shift to intersect the demand/supply curve at a new equilibrium point.
In other words, although both suppliers and buyers are price-takers they both influence price and quantity bought and sold, at the aggregate level.