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
What is the cause of entry-wound blackening in firearm injury? 
Select and explain. 
A. Flame, B. Smoke, C. Hot gases, D. Unburned powder
B: Smoke
Answer: B: Smoke 
Explanation: In firearm injury, entry-wound blackening is due to the smoke produced by completely burned paicles coming out from the barrel of the firearm weapon. It is seen up to 30 cm from the firearm. Ref: Essentials of Forensic Medicine and Toxicology By Dr K S Narayan Reddy, 27th Edition, Pages 187-8, 190