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: Pharmacology
Longest acting nitroglycerine preparation is: 
Select and explain. 
A. Glyceryl trinitrate, B. Amyl nitrite, C. Penta erythrital tetranitrate, D. Isosorbide dinitrate
C: Penta erythrital tetranitrate
Answer: C: Penta erythrital tetranitrate 
Explanation: None