Fill in the blank with the most appropriate word.
_____ they go to Australia last month?
A verb is used to express an occurrence, action, or state. It is the grammatical centre 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 last month indicates past tense.
The other options are wrong as the main verb is its first form (go).
The correct answer is D)did