This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
[{'content': 'Fast fatigable motor unit are recruited \nSelect and explain. \nA. First, B. Last, C. During active pa of contraction, D. During relaxation', 'role': 'user'}, {'content': "Answer: B \nExplanation: White muscle fibers are the fast fatigable motor units and are recruited last Red muscle fibers are rich in mitochondria and hence don't get fatigue soon Ref:Guyton and Hall textbook of medical physiology 12th edition,page number:91,92,93", 'role': 'assistant'}]