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
Purpose of liners and bases is/are: 
Select and explain. 
A. Pulp protection from thermal and chemical agents, B. Pulp protection from mechanical and electrical agents, C. Pulp medication, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Many restorative dental materials that provide excellent properties for the bulk of a dental restoration may not protect the dental pulp during setting or during cyclic thermal or mechanical stressing. Pulpal protection requires consideration of:

Chemical protection.
Electrical protection.
Thermal protection.
Pulpal medication.
Mechanical protection. 

Liners and bases are materials placed between dentin (and sometimes pulp) and the restoration to provide pulpal protection or pulpal response.