Data on the Unemployment Rate in the U

Data on the unemployment rate in the U.S.since 1960 show that the economy

A) always has some unemployment and that the amount stays constant from year to year.
B) always has some unemployment and that the amount changes from year to year.
C) sometimes has some unemployment and that the amount stays constant from year to year.
D) sometimes has some unemployment and that the amount changes from year to year.