Fill in the blank with the most appropriate word:The Flash's concert ________ fantastic 3 years ago.

Answer: Option A

The sentence refers to an event that took place in the past, specifically 3 years ago.
Past simple tense is used to describe actions or events that happened at a specific time in the past.
The subject "The Flash's concert" is singular, so the correct verb form is "was."
Therefore, the correct sentence is: The Flash's concert was fantastic 3 years ago.