Which of the following sets of data does not contain an outlier?
A) 45, 45, 45, 45, 35, 45
B) 6, 7, 5, 8, 9, 1
C) 25, 33, 29, 31, 33, 33, 78, 28
D) 101, 99, 98, 111, 101, 101, 103