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
What is PULP cap? 
Select and explain. 
A. Capping of the exposed vital pulp with a thin layer of inert lining or base material, B. Capping of exposed vital pulp tissue by placing a layer of mineral trioxide aggregate (MTA) or calcium hydroxide, C. A method of isolation used during root canal treatment, D. An early stage of tooth development
B: Capping of exposed vital pulp tissue by placing a layer of mineral trioxide aggregate (MTA) or calcium hydroxide
Answer: B: Capping of exposed vital pulp tissue by placing a layer of mineral trioxide aggregate (MTA) or calcium hydroxide 
Explanation: None