This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Muscle, Subject name: Physiology
[{'content': 'Which of the following best describes muscle B compared with muscle A? \nSelect and explain. \nA. Adapted for rapid contraction, B. Composed of larger muscle fibers, C. Fewer mitochondria, D. Innervated by smaller nerve fibers', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Muscle B is characteristic of a slow-twitch muscle (type 1) composed of predominantly slow-twitch muscle fibers. These fibers are smaller in size and are innervated by smaller nerve fibers. They typically have a more extensive blood supply, a greater number of mitochondria, and large amounts of myoglobin, all of which suppo high levels of oxidative phosphorylation.', 'role': 'assistant'}]