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
Lancefield 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. Staining properties
C: Group C carbohydrate antigen
Answer: C: Group C carbohydrate antigen 
Explanation: β hemolytic Streptococcus is classified to group A-V based on C carbohydrate antigen (Lancefield classification)
M protein is used to further classify group A Streptococcus (Griffith typing).

Ref: Apurba Sastry’s Essentials of Medical Microbiology 1/e p221, Ananthanarayan 9/e p209