[单选题]
某老年人牙龈退缩的牙面中未患龋牙面有40个,患根面龋的牙面10个,因根龋充填的牙面10个,该老年人根龋指数为()
A.20%
B.25%
C.33%
D.37%
E.40%
参考答案与解析: