The correct answer is a.: specific.
This structure (this +adj) requires an adjective and the only adjective is in a., the other options are verbs or nouns and are not correct.
(i will use an example cause this is not me xD and i hope this helps you)
An object that I feel that symbolizes a time when I was younger, will be a parrot. I think a parrot symbolizes me when I was younger is because I used to always repeat almost everything that people say. Even if someone I didn't know says something, I would repeat it and I would get in trouble. Another reason why I think parrots symbolized my younger self is because I really liked bright colors all around me. My room was colorful, my drawings were colorful, and my clothes were colorful, just like parrot's feathers, they are different and colorful. One last reason is because just how parrots live and like the tropical weather, I would always want to go somewhere tropical and hot, for an example, Florida. These are my reasons why I think a parrot symbolized my younger self.
Answer & Explanation:
It honestly means a lot to me because I can really relate. The quote is the truth because if you've already tried multiple times to do the same thing over and over again with no successes, there's no point. You are just forced to move on to something new. Also, the insanity part may not even be theoretical because I'm sure that many people have seriously gone insane from repeating the same words and actions all throughout their lives.
I hope this helps...have an awesome day!! :>
B. a German legend
^.^ Your welcome. <3