Lancefield grouping of streptococci is done by using-: (A) M Protein, (B) Group C peptidoglycan cell wall, (C) Group C carbohydrate antigen, (D) Staining properties
Answer is C. 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