The relative pronoun “which” can be singular or plural. Conjugate the verb to match the antecedent (noun or nouns, or noun phrase or phrases) that the pronoun replaces.
In a multiple-choice question stem, the antecedent often appears as the answer (or answers) to the question. This means we conjugate the verb depending on the number of answers we desire from students.
- Which of the following is true? (We expect students to select one answer.)
- Which of the following are true? (We expect more than one answer from students.)