We know that the anthology was shortened, but it still had some quality that probably wasn't desired. We can sense from that that this quality was connected to having too many words, so we need to seek a negative word describing that.
Out of possible choices, there are two connected to using too much words: choice (C), "loquacious," and choice (E), "prolix."
"Loquacious" means "talkative" and it doesn't fit here, since it's associated only with speaking, not writing. "Prolix" means "using too many words" and it fits in the blank, since it's more general. Looking at the other answers, we might be tempted to use the word in choice (B), "pretentious." It means "making unjustified claims of value" and we can imagine from the context that the author was making the claims that his anthology was poetic, while in reality it wasn't. However, it doesn't refer directly to the length of the piece, so it's not correct.