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
World Health Day is celebrated on: 
Select and explain. 
A. 1st December, B. 31st may, C. 7th april, D. 8th may
C: 7th april
Answer: C: 7th april 
Explanation: 7th April