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
Chronic bronchitis can be a premalignant condition, which involves: 
Select and explain. 
A. Columnar to squamous, B. Squamous to columnar, C. Squamous to cuboidal, D. Cuboidal to squamous
A: Columnar to squamous
Answer: A: Columnar to squamous 
Explanation: 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;