D. Quixotic
It’s a support because of the semicolon.
We want an idea that means something not real, because it says “Reality was Not”, so the blank should be something, let’s say, a fantasy or idealistic.
A means Verbose
B means Cheerful
C means Fervid
D means Idealistic
E means Trifling
Side note! As an Esperanto advocate I don’t think if it is quite quixotic. 
Nicely done!