This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiration, Subject name: Pathology
[{'content': 'Chronic bronchitis can be a premalignant condition, which involves: \nSelect and explain. \nA. Columnar to squamous, B. Squamous to columnar, C. Squamous to cuboidal, D. Cuboidal to squamous', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) Columnar to squamous(Ref: Robbins 9th/pg 679)Chronic bronchitis is an example of squamous metaplasia in which normal columnar epithelium of respiratory tract is replaced by squamous epithelium;', 'role': 'assistant'}]