What is the passive voice transformation of "They completed the project on time"?

The sentence "They completed the project on time" is in the active voice, where "they" is the subject performing the action. When transforming to the passive voice, the focus shifts to the object of the action, which is "the project." The correct transformation maintains the same meaning while restructuring the sentence so that the project is now the subject receiving the action.

In this case, "The project was completed on time by them" effectively conveys that the project is the focus and that the action of completing it was carried out by them. The use of "was completed" indicates that the action occurred in the past, corresponding to the original sentence's tense. The phrase "by them" identifies who completed the project, maintaining the original meaning.

The other transformations either change the tense, omit essential details, or alter the meaning inappropriately.