This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Muscles of Lower Limb, Subject name: Anatomy
[{'content': 'Chief Extensor at knee joint is \nSelect and explain. \nA. Biceps femoris, B. Quadriceps femoris, C. Semitendinosus, D. Semimembranosus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Quadriceps femoris is knee Extensor. Hamstrings (Biceps femoris long head, Semitendinosus, Semimembranosus and Adductor magnus) are Knee Flexors.', 'role': 'assistant'}]