Fill in the blank with the most appropriate word.
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 is used in the formation of tenses, moods, tones, etc.
Option C is correct as the sentence talks about a general fact. Therefore, only simple present tense in the passive form can be used.
The other options are wrong as no other tense can be used here.
The correct answer is C)is celebrated