Which choice could be modeled by a linear function? A. The amount, y, of radioactive material remaining after x years when decay occurs at a rate of 30% each year.
B. The amount of money, y, in an amount after x years earning 4% interest compounded annually.
C. The monthly cost, y, to use a cell phone for x minutes at a rate of 4 cents per minute.
D. The height, y, of a ball after bouncing x times, if each bounce reaches 2/3 the previous height.