The correct option is B i.e. were unique for theirs.
<h3>What is a subject-verb agreement?</h3>
The matching of a sentence's subject and verb in tense, aspect, and mood, also known as the number, person, and gender, is known as subject-verb agreement or "subject-verb concord".
Only the verb be altered depending on whether the sentence is in the first, second, or third person in English, which does not employ grammatical gender aside from pronouns. Accordingly, the majority of subject-verb agreements in English are quantified: if the subject is singular, the verb must also be singular; if the subject is plural, the verb must also be many. Even this, though, can be perplexing because the first-person singular ("I climb the fence") and first-person plural ("We climb the fence") verb tenses are the same.
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