Fill in the blanks with the most appropriate words.
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 sentence is about something in general. Therefore, only simple present tense can be used.
The other options are wrong as no other tense can be used here.
The correct answer is C) am/am