Final answer:
The phrase that would add verbal irony to the paragraph is "aren't sufficiently brief" (C), as it humorously contradicts the intent of editing for brevity by implying that even after editing, the text is still too long.
Step-by-step explanation:
The student is seeking a phrase that would add verbal irony to a paragraph about editing for brevity. Verbal irony is a figure of speech where what is said is the opposite of what is meant. Considering the context of the paragraph discussing trimming the fat off sentences to ensure conciseness, a phrase that highlights the opposite—such as stating something is not brief when in fact it is—would be ironically amusing.
Thus, the phrase "aren't sufficiently brief" (C) would be the best choice for adding verbal irony. This phrase suggests that despite the editing for brevity, the statements are still not brief enough, contrasting with the purpose of editing. It emphasizes the expectation that editing should render text to its shortest effective length, and to say the edited text is still not brief enough flips the expectation on its head in an ironic twist.