Final answer:
You should set a direct quote apart as a separate block of text when the quote is more than one sentence long, specifically longer than four lines for prose or three lines for poetry, according to MLA style guidelines.
Step-by-step explanation:
The correct answer to the question 'When should you set a direct quote apart as a separate block of text?' is c) The quote is more than one sentence long. In academic writing, a block quote is used to format direct quotations that are longer than four lines for prose or three lines for poetry. According to MLA style guidelines, a block quotation should be indented and set off in the text, and because setting off indicates quotation, quotation marks are not needed unless there is a quotation within the quotation.
To format a block quotation, you can justify the text and indent it. This will be clear it is a block quotation in that it is set aside from the rest of the text. Remember that block quotations should be used sparingly and should only quote as much as is necessary to support the thesis or main idea of the paragraph.