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: Dental
Principle secretory cells found in the single layer outlining the pulp (Ourtermost zone of pulp) 
Select and explain. 
A. Fibroblasts, B. Odontoblast, C. Ameloblast, D. Undifferentiated cells
B: Odontoblast
Answer: B: Odontoblast 
Explanation: The outermost odontoblast layer,(Single layer outlining pulp ) contains odontoblasts as principal secretory cells for Dentin while they also secrete Collagen Type 1 and type 5 collagen fibers