Select the option that correctly fills the gap: Neither the principal nor the teachers _______ aware of the students' plan to boycott the examination.

With 'neither...nor' constructions, the verb agrees with the subject closest to it. Here, 'teachers' (plural) is closest to the verb, so the plural verb 'were' is correct. 'Was' would be used if the singular subject were closer, and 'are' is incorrect tense for a past context.