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: Microbiology
Lance field grouping of streptococci is done by using : 
Select and explain. 
A. M protein, B. Group C peptidoglycan cell wall, C. Group C carbohydrate antigen, D. M antigen
C: Group C carbohydrate antigen
Answer: C: Group C carbohydrate antigen 
Explanation: Lancefield classification
Classification of β hemolytic streptococci into Group A to V (except I, J) on the basis of group specific C carbohydrate.
Griffith classification
Serological typing of Group A Streptococcus pyogenes on the basis of M proteins into types 1, 2, 3 etc.
Group C Carohydrate

Present in middle layer of cell wall.
This antigen is an integral part of cell wall.
Serological grouping of streptococci depend on C carbohydrate for which it has to be extracted from cell wall.