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: Unknown
Craigia tube is used to differentiate between: 
Select and explain. 
A. Virulent and avirulent strains, B. Rough and smooth strains, C. Motile and non-motile strains, D. Capsulated and non-capsulated strains
C: Motile and non-motile strains
Answer: C: Motile and non-motile strains 
Explanation: None