Which choice could NOT be modeled by an exponential function? he amount, y, of radioactive material remaining after x years when decay occurs at a rate of 30% each year the monthly cost, y, to use a cell phone for x minutes at a rate of 4 cents per minute the amount of money, y, in an account after x years earning 4% interest compounded annually the height, y, of a ball after bouncing x times, if each bounce reaches half of the previous height