Which sentence uses the time-related term correctly?
A: Peter enjoys reading about American history, especially the last 40 years, or four decades.
B: Peter enjoys reading about American history, especially the last 40 years, or four millennia.
C: Peter enjoys reading about American history, especially the last 40 years, or four centuries.
D: Peter enjoys reading about American history, especially the last 40 years, or four eras.