Identify the lower quartile (Q1), the median (Q2), and the upper quartile (Q3) for this data set.

{6, 7, 9, 10, 12, 14, 15, 17, 19, 21}

A) Q1 = 9, Q2 = 13, Q3 = 17
B) Q1 = 6, Q2 = 13, Q3 = 21
C) Q1 = 6, Q2 = 14, Q3 = 19
D) Q1 = 9.5, Q2 = 12.5, Q3 = 18.5