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
Dried semen stains on clothes are identified by: 
Select and explain. 
A. Spectrometry, B. Ultravoilet rays, C. Infrared rays, D. Magnifying lens
B: Ultravoilet rays
Answer: B: Ultravoilet rays 
Explanation: Ultravoilet rays