The correct answer to this question is option B “were unique for their” because the subject must agree with its verb and the pronoun with its antecedents.
There are some rules for subject-verb agreement;
A singular subject goes with a singular verb but a plural subject goes with a plural verb. E.g. The List of items is on the desk.
If there are two singular subjects that are connected by “or”, “either/or”, and “neither/nor”, they require a singular verb. E.g. Neither Arnold nor Martin is available.
If there are two or more subjects that are connected with “and”, one must use a plural verb. E.g. Pasta and burgers are my favorite.
To learn more about the subject-verb agreement, visit;
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