Graphs simplify economic ideas and make them more concrete. Consider the data available on these two Web sites:

• www.eia.gov/dnav/pet/pet_pri_gnd_a_epmr_pte_dpgal_w.htm provides data on the retail price of gasoline (what we pay at the pump) for both the United States overall and for different regions and states.

• www.eia.gov/dnav/pet/PET_CONS_REFMG_D_NUS_VTR_MGALPD_M.htm provides data on gasoline sales for the United States.

If you were to use a graph to explain changes in these data over time, would you use a graph of the demand curve, a graph of the supply curve, or a graph of a market? Write a paragraph to explain your thinking.