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: Surgery
Necrosis of entire skin thickness and variable thickness of underlying subcutaneous tissue is: 
Select and explain. 
A. 1st degree frostbite, B. 2nd degree frostbite, C. 3rd degree frostbite, D. 4th degree frostbite
C: 3rd degree frostbite
Answer: C: 3rd degree frostbite 
Explanation: 1st degree frostbite is hyperemia and edema of skin.
2nd degree frostbite is hyperemia, vesicle formation and partial thickness necrosis of skin.
3rd degree frostbite is necrosis of entire skin thickness and variable thickness of underlying subcutaneous tissue.

4th degree frostbite is necrosis of entire thickness of skin and all underlying structures, leading to gangrene of the affected part.