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: Microbiology
Which of the following statements is true about BCG vaccination? 
Select and explain. 
A. Distilled water is used as diluent for BCG, B. The site of injection should be cleaned with spirit, C. Mantoux test becomes positive after 48 hours of vaccination, D. WHO recommends Danish 1331 strain for vaccine production
D: WHO recommends Danish 1331 strain for vaccine production
Answer: D: WHO recommends Danish 1331 strain for vaccine production 
Explanation: "Danish 1331" is the strain recommended by WHO for the production of vaccine. Since the 1967, the "Danish 1331" has been in use. The quality is regularly kept in check by the International Reference Centre at Copenhagen. The diluent used in the BCG vaccine is normal saline and not distilled water. The site of injection should be cleaned with normal saline before administering the injection. The Mantoux test becomes positive after a period of 8 - 14 weeks. Ref: Park's Textbook of Preventive and Social Medicine 19th edition; pages 160 - 163.