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
The connective tissue cells of pulp are derived from 
Select and explain. 
A. The pool of undifferentiated mesenchymal cells, B. The pool of fibroblasts, C. The pool of undifferentiated ectodermal cells, D. The pool of osteoblasts
A: The pool of undifferentiated mesenchymal cells
Answer: A: The pool of undifferentiated mesenchymal cells 
Explanation: None