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: Forensic Medicine
In a case of suspected poisoning, the preservative used for vitreous during autopsy is: 
Select and explain. 
A. Fluoride, B. HC1, C. Phenol, D. Xylol
A: Fluoride
Answer: A: Fluoride 
Explanation: Fluoride should be added to urine, CSF, and vitreous humour if alcohol estimation is required, and also to samples for analysis for cocaine, cyanide and CO. Sodium or potassium fluoride should be used for preserving blood. Ref: The essentials of forensic medicine and toxicology by Dr K S Narayan Reddy, 27th edition, Page 111.