We replace something old with something new.
- The Mayor has replaced all the old school buses with new ones.
When the sentence is written in the passive voice, "by" is used.
- All the old school buses have been replaced by new ones.
- All the old school buses have been replaced by the Mayor.
But what about a sentence in the passive voice that mentions the object that is substituted and the subject who performed the action, the agent? Which preposition should be used?
- All the old school buses have been replaced by the mayor ....... new ones.