Calculate the mean, median, and mode of the following population of numbers: 5, 5, 5, 9, 9, 5, 4, 6, 13, 9.

a) Mean: 7.5, Median: 6.5, Mode: 5
b) Mean: 6.5, Median: 7.5, Mode: 9
c) Mean: 6.5, Median: 6.5, Mode: 5
d) Mean: 7.5, Median: 7.5, Mode: 9