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
Which of the following stage of tooth formation is characterized by the commencement of mineralization and root formation: 
Select and explain. 
A. Bud stage., B. Cap stage., C. Bell stage., D. Advanced bell stage.
D: Advanced bell stage.
Answer: D: Advanced bell stage. 
Explanation: Mineralization and root formation is the characteristic feature of Advanced bell stage.