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 nitroglycerin is: 
Select and explain. 
A. Amyl nitrite., B. Penta erythrital tetranitrate., C. Isosorbide dinitrate, D. Isosorbide mononitrate.
B: Penta erythrital tetranitrate.
Answer: B: Penta erythrital tetranitrate. 
Explanation: None