A. Correct because the firm's supply curve should measure the quantity the firm is willing to supply at various prices. Also, the market supply curve is the sum of the supply curves of the individual firms.

B. Incorrect because the effects of the actions of the buyers on price and quantity are described by the demand curve, not the supply curve: The demand curve shows the highest price consumers would be willing to pay for each additional unit. In effect, the demand curve is the willingness of consumers to pay for each additional unit. C. Incorrect because the supply curve shows the lowest price (not the highest price) sellers are willing to accept for each quantity.