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: Medicine
What is drug of choice for ulcerative colitis - 
Select and explain. 
A. Salazopyrine, B. Predinisolone, C. Sulphasalazine, D. 5-amino salicylic acid
D: 5-amino salicylic acid
Answer: D: 5-amino salicylic acid 
Explanation: None