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 liners when exposed to oral fluids result in diminishment of their antimicrobial effectiveness? 
Select and explain. 
A. MTA, B. Calcium hydroxide, C. Both, D. None
C: Both
Answer: C: Both 
Explanation: MTA and calcium hydroxide undergo a transformation of hydroxide to calcium carbonate from exposure to carbon dioxide in the blood and oral fluids, causing their antimicrobial effectiveness to diminish.