question: Double-ended Gracey curettes are paired in the following manner,except:
opa: Gracey #1-2 and #3-4: Anterior teeth
opb: Gracey #5-6: Anterior teeth and premolars
opc: Gracey #7-8 and #9-10: Posterior teeth, mesial
opd: Gracey #11-12: Posterior teeth, mesial