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': 'Physiological unlocking is caused by - \nSelect and explain. \nA. Popliteus, B. Rectus femoris, C. Semimembranosus, D. Sartorius', 'role': 'user'}, {'content': 'Answer: A \nExplanation: During last stages of extension, femur rotates medially on tibia due to quadriceps femoris to lock the knee joint. Femur rotates laterally on tibia during flexion. \nQuadriceps femoris- Vastus medialis, vastus lateralis, vastus intermedius, rectus femoris. Unlocking occurs with popliteus.', 'role': 'assistant'}]