This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Joints, Subject name: Anatomy
[{'content': 'Which is an unlocker of knee? \nSelect and explain. \nA. Popliteus, B. biceps femoris, C. Sartorius, D. Gastrocnemius', 'role': 'user'}, {'content': "Answer: A \nExplanation: ANSWER: (A) PopliteusREF: Gray's anatomy 39th ed p. 1465,1482-83* Locking or screw home mechanism: Conjuct medial rotation of femur on tibia in later stages of extension due to quadriceps femoris locks the knee joint.Unlocking of knee joint: At beginning of flexion from full extension with foot flexed, lateral rotation by Popliteus muscle unlocks the joint.", 'role': 'assistant'}]