An aggregate demand (AD) curve shows the a. amount of a particular good people are willing and able to buy at a particular price, ceteris paribus. b. real output (Real GDP) people are willing and able to sell at different price levels, ceteris paribus. c. real output (Real (GDP) people are willing and able to buy and to sell at different price levels, ceteris paribus. d. real output (Real GDP) people are willing and able to buy at different price levels, ceteris paribus.