You are presented with the quiz "What occurs when many muscles contract a little bit all at once?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "shivering occurs when many muscles contract a little bit all at once" and "involuntary contractions, shivering, cause the production of heat". So, what's the best answer to the question?

Choose from: [-] the production of cells; [-] preventing heat transfer; [-] To keep their body heat.; [-] the production of heat; [-] Generating heat; [-] recovery time from fatigue; [-] the production of cold; [-] the production of skin;
The answer is:
the production of heat