A 55-year-old man, surnamed Huang, can surprisingly lift 50kg of stones with his feet and carry them, along with two dumbbells in his hands for 200 meters in a village in Chengdu, Sichuan province. Huang said that he's walked with stones on his feet every day for years as a way to exercise and he's "worn out" seven pairs of stones.
How many pairs of stones has been worn out by the man?
A. 6
B. 7
C. 8