Which sentence is passive voice?
1. The clerk made five errors.
2. Susan had been in sales for five years.
3. She asked for an adjustment.
4. The report was completed by the entire team.
Ask yourself about who is doing that action -- if the subject is doing the action, then the verb is active. If the subject is NOT doing the action (if the subject is "acted upon" by someone/something else), then the verb is passive.
To determine which sentence is in the passive voice, we need to look for a form of the verb "to be" (e.g., was, were, has been, had been) followed by a past participle.
The sentence in the passive voice is:
4. The report was completed by the entire team.
In this sentence, "was" is a form of the verb "to be," and "completed" is the past participle of the verb "complete." The focus in this sentence is on the report being completed by the team, rather than who completed it.