Select the correct passive form of the given sentence.
Our rivals must have spread this rumour.

Correct option is A

The correct passive form of "Our rivals must have spread this rumour" is “a” "This rumour must have been spread by our rivals." This maintains the modal verb "must" and the perfect tense in passive voice.
· Active Voice- Active voice is a grammatical structure in which the subject of the sentence performs the action expressed by the verb.
· Passive Voice- Passive voice refers to a grammatical construction where the subject of a sentence undergoes an action rather than performing it. In passive voice sentences, the emphasis is on the recipient or object of the action.
To convert an active voice sentence to passive voice, follow these steps:
· Identify the subject, the verb, and the object in the active voice sentence.
· The object of the active voice sentence becomes the subject of the passive voice sentence.
· Change the verb to its past participle form. If necessary, use a form of "be" (is, are, am, was, were, be, been) and the past participle of the main verb. For modals (like might, may, can, could, etc.), the structure is usually modal + "be" + past participle.
· The subject of the active sentence becomes the object of the passive sentence (or is dropped).
Conversion rule:
Subject + must + have + V3 + object →← Object + must + have + been + past participle + by + subject.