The suitable set of readers for a formal essay on effects of advertising campaign in the aforementioned conditions will be the general audience. Hence, option A holds true.
A reader is someone who reads any form of literary composition. However, the meaning of a reader from an author's point of view is the one to whom the author wants to persuade and read his or her literary composition.
When the target reading audience is the public, then in such case the composition or the essay written by the author can be read by anyone. In such case, the profile of the reader does not matter for the author.
Hence, option A is correct regarding the significance of a reader of a formal essay on the advertising campaign.
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