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 classification based on: 
Select and explain. 
A. M protein, B. Carbohydrate antigen, C. Cell wall peptidogglycan, D. T protein
B: Carbohydrate antigen
Answer: B: Carbohydrate antigen 
Explanation: Carbohydrate antigen