The dot plots represent the distributions of values in Data Set A and Data Set B.
Data Set A has values: 1, 2, 2, 3, 3, 3, 4, 4, 5.
Data Set B has values: 1, 1, 1, 2, 2, 3, 4, 5, 6.

Which of the following statements must be true?
I. The median of data set A is greater than the median of data set B.
II. The mean of data set A is equal to its median.