This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Larynx, Subject name: ENT
[{'content': 'Cotton&;s grading is used for \nSelect and explain. \nA. Subglottic stenosis, B. Laryngeal carcinoma, C. Superior nerve palsy, D. Voice abuse', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Subglottic stenosis is graded according to the Cotton-Myer classification system from one to four based on the severity of the blockage. Grade 1 - <50% obstruction Grade 2 - 51-70% obstruction Grade 3 - 71-99% obstruction Grade 4 - no detectable lumen Ref: Internet sources- Wikipedia', 'role': 'assistant'}]