Why does muscle activity affect the temperature of the body?

a. The rate of chemical reactions increases in muscle fibers during contraction, so the rate of heat production also increases.
b. Muscle contraction generates pyrogens which reset the body's internal thermostat to a higher temperature.
c. Muscle activity directs more warm blood to the muscles away from the central core causing a cooling effect on your internal organs.
d. Increased muscle activity causes a rise in adipose stores which increases the insulation value of the body.