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| OAU | OB | OBA | OBAFGKM | OBC | OBCP |
| OBD | OBEM | OBF | OBFLW | OBGYN | OBH |
| OBI | OBIC | OBIR | OBL | OBM | OBP |
| OBQ | OBR | obs | OBT | OBU | OBX |
| OC | OCA | OCAD | OCAD U | OCAS | OCAST |
| OCB | OCC | OCCAM | OCCB | OCCC | OCCS |
| OCD | OCE | OCEANAV | OCED | OCF | OCI |
| OCID | OCL | OCLC | OCLIPS | OCLV | OCM |
| OCMB | OCMD | OCN | OCNMAP | OCO | OCP |
| OCPA | OCQ | OCR | OCRD | OCRE | OCRM |
| OCS | OCSAB | OCSEAP | OCSG | OCSH | OCSHA |
| OCSI | OCSN | OCT | OCTG | OCU | OCUA |
| OCUC | OCV | OCXO | OCZ | OD | ODA |
| ODAA | ODAB | ODAR | ODAS | ODAT | ODATA |
| ODC | ODCB | ODCSINT | ODCSOPS | ODD | ODE |
| ODEND | ODEPR | ODI | ODMR | ODP | ODR |
| ODS | ODT | ODTU | ODU | ODW | ODX |