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
FC FFG, FFFG ... used to describe- 
Select and explain. 
A. Primer, B. Cartridge, C. Black gunpowder, D. Base of firearms
C: Black gunpowder
Answer: C: Black gunpowder 
Explanation: Depending on fineness, the black gun powder is designated as FG, FFG, FFFG etc (F = fineness).