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: Surgery
[{'content': 'Thomas test is used for testing \nSelect and explain. \nA. Knee flexion, B. Knee extension, C. Hip flexion, D. Hip extension', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Hip flexion', 'role': 'assistant'}]