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
Which of the following best describes muscle B compared with muscle A? 
Select and explain. 
A. Adapted for rapid contraction, B. Composed of larger muscle fibers, C. Fewer mitochondria, D. Innervated by smaller nerve fibers
D: Innervated by smaller nerve fibers
Answer: D: Innervated by smaller nerve fibers 
Explanation: 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.