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 is used in the formation of tenses, moods, tones, etc.
Option D is correct as the sentence is in the passive voice and sometimes indicates the use of are invited.
The other options are wrong as no other tense can be used here.
The correct answer is D) are invited