A verb is used to express an occurrence, action, or state. It is the grammatical center of the predicate in a sentence.
An auxiliary verb is a verb which gives is used in the formation of tenses, moods, tones, etc.
Option D is correct as neither and there indicate the use of the verb be in the past participle form.
The other options are wrong as no other tense can be used here.
The correct answer is D) was