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
Faint letter mark can be made visible by : 
Select and explain. 
A. Infrared photography, B. Spectrophotometer, C. Ordinary light, D. X-ray
A: Infrared photography
Answer: A: Infrared photography 
Explanation: A i.e. Infrared photography