This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Replacement of columnar epithelium in respiratory tract to squamous epithelium is - 
Select and explain. 
A. Hyperplasia, B. Hypoplasia, C. None of the above, D. Metaplasia
D: Metaplasia
Answer: D: Metaplasia 
Explanation: Metaplasia
o Metaplasia is a reversible change in which one differenated cell type is replaced by another differenated cell type.
o Metaplasia represents an adapve substuon of cells that are sensive to stress by cell types beer able to withstand the adverse environment,
o Metaplasia may be of two types