The following stem-and-leaf plot shows the on-record attendance for regional charity drive meetings.
3 | 1 2 4 8 8 9
4 | 0 3 5 7
5 | 6 6
6 | 0 0 1 3 4 8
7 | 0 1 3 4 4 4 7

What is the mode of these values?
A. 56
B. 74
C. 60
D. 38 ​