單項選擇題在對老年人進行口腔健康檢查時發(fā)現(xiàn)某老年人牙齦退縮的牙面中未患齲牙面有40個,患根齲的牙面10個,因根齲充填的牙面10個,該老年人根齲指數(shù)為()

A.20%
B.25%
C.33%
D.37%
E.40%