This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax, Subject name: Anatomy
[{'content': 'Which of following is attached to first rib? \nSelect and explain. \nA. Scalenus posterior, B. Serroatus posterior superior, C. Scalenus medius, D. None of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Scalenus mediums attached to the first rib. B D CHOURASIAS HUMAN ANATOMY UPPER LIMB THORAX VOLUME, 1 SIXTH EDITION, Page no,199', 'role': 'assistant'}]