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: Pathology
Which of the following is the most commonly used 'fixative' in diagnostic pathology? 
Select and explain. 
A. Formaldehyde, B. Ethyl alcohol, C. Mercuric chloride, D. Picric acid
A: Formaldehyde
Answer: A: Formaldehyde 
Explanation: Formaldehyde is the most commonly used fixative in diagnostic pathology. Ref: Surgical Pathology Dissection: An Illustrated Guide By William H. Westra, Page 14.