Ten students were sampled at random from a student population. Each was asked how many courses he or she was planning on studying in the upcoming year. The following is a list of the reported data values:
1, 2, 2, 3, 4, 5, 5, 5, 5, 6
What's the standard deviation for the data values?
A. 1.6
B. 1.687
C. 2.56
D. 2.84