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
Di's collar is seen in the following condition: 
Select and explain. 
A. Firearm entry, B. Firearm exit wound, C. Both of the above, D. None of the above
A: Firearm entry
Answer: A: Firearm entry 
Explanation: After the bullet has perforated the skin, the elasticity of the skin causes the skin defect to contract. The skin is abraded (abrasion collar) around the hole due to rubbing of the gyrating body of the bullet against the inveed epidermis and heat of the bullet. A black coloured ring "grease or di collar" (bullet wipe soiling) is seen as narrow ring of skin, lining the defect, and is sharply outlined. This is caused from the removal of substances from the bullet as it passes through the skin. It is more marked in a distant shot. Ref: The Essentials of Forensic Medicine and Toxicology by K S Narayan Reddy, 27th edition, Page 196.