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: Social & Preventive Medicine
Mistuda reaction is read at 
Select and explain. 
A. 21st day, B. 10th day, C. 3rd day, D. 45th day
A: 21st day
Answer: A: 21st day 
Explanation: None