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: Radiology
The ingredient of the fixing solution (fixer) of the X-ray is: 
Select and explain. 
A. Hydroquinone, B. Elon, C. Sodium bisulphate, D. Acetic acid
D: Acetic acid
Answer: D: Acetic acid 
Explanation: None