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 the subject is 'I' and the present simple tense is used for a present state, habits,routines, jobs, hobbies or expressing possession, generalisations , scientific statements.
The other options are wrong as the subject is not plural and the past simple tense is used for an action or a series of actions in the past.
The correct answer is D)don't;is