Final answer:
The festival is held on the same day every year.
Step-by-step explanation:
The correct answer is a is held.
The verb is held indicates that the festival takes place on the same day every year. This construction is in the present tense and the third person singular form. Therefore, option a shows the correct verb form of to hold.
For example, the Strawberry Festival is held on the first Saturday of June every year.
Learn more about Verb tense in English