Why Is Heat Shown Flowing from the Worker in the Illustration

Why is heat shown flowing from the worker in the illustration below?

A) The worker was exposed to the sun while working outside and simply got hot.
B) The conversion of metabolic energy into muscle contraction is not 100 percent efficient and some of the energy is lost as heat.
C) Using a hammer, paintbrush, or any other tool generates friction and heat in the arm that must be lost to maintain homeostasis.
D) Energy and matter are equivalent; the conversion of the worker's body mass to kinetic energy requires a reduction of body mass and is indicated by the outflow arrows.