Which one of the following data sets has more than one mode?
A. {10, 20, 30, 30, 40, 50, 50)
B. {10, 20, 30, 40, 50, 70, 70)
C. {20, 20, 30, 30, 30, 40, 40}
D. {10, 20, 30, 40, 50250, 70)