This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
[{'content': 'Chief extensor of knee joint in hip flexion is \nSelect and explain. \nA. Rectus femoris, B. Vastus medialis, C. Vastus latralis, D. Hamstrings', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A. i.e. Rectus femoris', 'role': 'assistant'}]