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
FG, FFG, FFFG ... used to describe: 
Select and explain. 
A. Primer, B. Caridge, C. Black gunpowder, D. Base of firearms
C: Black gunpowder
Answer: C: Black gunpowder 
Explanation: C i.e. Black gunpowder