Answer the following question given this paragraph: Mammals generate heat mainly by keeping their metabolic rate high. The cells of mammals have many more mitochondria than the cells of other animals. The extra mitochondria generate enough energy to keep the rate of metabolism high. Mammals can also generate little bursts of heat by shivering. Shivering occurs when many muscles contract a little bit all at once. Each muscle that contracts produces a small amount of heat. Q: Mammals generate heat primarily by maintaining a high rate of what? Choices: - reproduction - respiration - movement - metabolism A:
A:
metabolism