How do the muscles in thermoregulation?
muscles produce oil that burns in the presence of oxygen.
muscles undergo a chemical reaction that absorbs heat.
muscles break down carbon dioxide, producing heat.
muscles contract rapidly, producing heat.

Muscles contract rapidly, producing heat.

Explanation:

Thermoregulation can be defined a process, which involves maintenance of body's core internal temperature. During cold, muscles help in thermoregulation as they generate heat to make body warm by contracting rapidly.

Muscle contraction uses energy from hydrolysis of ATP molecules, during which some energy gets lost as heat. This energy is used to generate heat for thermoregulation.

Thus, the correct answer is option). 'muscles contract rapidly, producing heat.'

on my test it was D-Muscles contract rapidly, producing heat.

the answer is d. chordata