This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Joints of Lower Extremity, Subject name: Anatomy
[{'content': 'Unlocking of knee: \nSelect and explain. \nA. Popliteus, B. Quadriceps femoris, C. Semitendinosus, D. Semimembranosus', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) PopliteusRef: BDC vol II /155* Quadriceps femoris is the main and only extensor of knee.* It produces locking action as a result of medial rotation of the femur during the last stage of extension.* To reverse this lock popliteus muscle comes into action and do so by the lateral rotation of femurRemember: Lock is: Quadriceps femoris muscle and, Key is popliteus muscle.Muscles producing movements at the knee jointMovementPrincipal musclesA. Flexion* Biceps femoris* Semitendinosus* SemimembranosusB. ExtensionQuadriceps femorisC. Medial rotation of flexed leg* Popliteus* Semimembranosus* SemitendinosusD. Lateral rotation of flexed leg* Biceps femorisAlso know* Quadriceps femoris incudes: Vastus Lateralis, Vastis Medialis, Vastus Intermedius.* Rectus femoris is also known as "kicking muscle"', 'role': 'assistant'}]