A man covers a total distance of 100 km on bicycle. For the first 2 hours, the speed was 20 km/hr and for the rest of the journey, it came down to 10 km/hr. The average speed will be
A. 12 1/2 km/hr
B. 13 km/hr
C. 15 1/8 km/hr
D. 20 km/hr