This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ballistics, Subject name: Forensic Medicine
FG, FFG, FFFG is used to indicate: 
Select and explain. 
A. Caridge, B. Black powder size, C. Base of gun, D. Wadding of caridge
B: Black powder size
Answer: B: Black powder size 
Explanation: Black Gun Powder: Described as FG, FFG, FFFG, FFFFG depending on the fineness of the grain. The finer grains have more number of 'F'