At the county fair, one of the more popular booths is the Crawfish Race booth. In the last race, the champion crawfish traveled 8 mm after the first second and 68 mm after twenty-nine seconds. Approximately what was the average rate of change for the distance covered during that time?
A. 28 mm per second
B. 0.47 mm per second
C. 2.14 mm per second
D. 60 mm per second