Well it isn't D and it has nothing to do with B even thought the Decoration involved and included slavery it isn't the main thing going on there.
Your answer is A
An intriguing plot, detailed characters, and an interesting rising action.
The answer is an appositive phrase. An appositive is an extra piece of detail or information describing in this case "lemon cake" and which the sentence still makes sense without. It still makes sense to say "<span>For my birthday, we baked a lemon cake." The "special treat" adds additional information about the "lemon cake."</span>
