Verb to be + Past Participle.
Past Participle examples:
| Verb in base form | Past Simple | Past Participle |
|---|---|---|
| develop | developed | developed |
| invent | invented | invented |
| write | wrote | written |
| break | broke | broken |
In passive voice we can sometimes mention who did the action. If you think it is really important to mention who is doing the action, then you have the choice of doing that using “by” and the subject.