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: Anatomy
All of the following are derivatives of connective tissue except? 
Select and explain. 
A. Endothelial cells, B. Clara cells, C. Fibroblast, D. Mast cells
B: Clara cells
Answer: B: Clara cells 
Explanation: None