解：∵OA⊥DA，CE⊥DA，∴∠CED=∠OAB=90°，∵CD∥OE，∴∠CDA=∠OBA，∴△AOB∽△ECD，∴ CE DE = OA AB ， 1.6 2 = OA 20 ，解得OA=16．故选D．
