单项选择题

A.有菌斑牙面数与总牙面数之比小等于10%
B.有菌斑牙面数与总牙面数之比小等于15%
C.有菌斑牙面数与总牙面数之比小等于20%
D.有菌斑牙面数与总牙面数之比小等于25%
E.有菌斑牙面数与总牙面数之比小等于30%