In long sentences always be aware of the main [subject] and [verb]. Once you establish their relation is ok, you move on. You should notice the word by which is leading you into a list. All list elements must be of the same word type, or follow the same syntax. The current list is made up of nouns, meaning option D marks the incorrect fragment.
A well-composed baroque opera achieves a delicate balance by focusing alternatvely on the aural, visual, emotional, and philosophical elements.