What Factor Would Explain Why, in a Cold Climate, Worker

What factor would explain why, in a cold climate, Worker A can raise their body temperature by four degrees by jogging on the spot or skipping with a rope, whereas Worker B can only raise their body temperature by two degrees?

A) Worker A is in better physical condition.
B) Worker B is an older worker.
C) Worker A is a non-smoker.
D) Worker B is female.