This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Upper Extremity, Subject name: Anatomy
[{'content': 'Axillary sheath is an extension of- \nSelect and explain. \nA. Pretracheal fascia, B. Prevertebral layer of deep cervical fascia, C. Investing layer of deep cervical fascia, D. None', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Prevertebral layer of deep cervical fascia 'Axillary sheath and fascia around trunk of brachial plexus are derived from prevertebral fascia (prevertebral layer of deep cervical fascia).'", 'role': 'assistant'}]