Answer:
The reason to use a direct quotation is:
c. when the words of an authority are needed to emphasize the point.
Step-by-step explanation:
Direct quotations are most effective when they come from a credible and authoritative source, and can be used to support an argument or emphasize a particular point. By quoting directly from an expert or a well-known authority on a subject, you can lend additional weight and credibility to your argument, and make your point more persuasive to your audience. However, it is important to use direct quotations judiciously and to always properly cite your sources to avoid plagiarism.