Over the last 80 years, the average annual U.S. inflation rate was about

a. 3.6 percent, implying that prices have increased 16-fold.

b. 4 percent, implying that prices have increased 17-fold.

c. 4 percent, implying that prices have increased 16-fold.

d. 3.6 percent, implying that prices increased about 17-fold.