Which of the following demonstrates correct use of a colon?

The use of a colon is appropriate in the given context of the correct choice. A colon is used to introduce a list, a quotation, or to emphasize a point. In this case, the sentence states "The report heading was promising: 'Sales up 15 percent.'" The colon efficiently introduces the quotation that elaborates on the statement about the report heading, indicating that what follows is directly linked to the preceding clause.

The other options demonstrate incorrect uses of punctuation. The second choice improperly uses a semicolon and a colon within the same sentence, which creates confusion instead of adding clarity. The third choice fails to follow the correct structure for introducing a quotation after "said," which requires a different punctuation mark or structure. The fourth choice incorrectly uses a dash to connect two independent clauses, which should be properly punctuated with a semicolon or a conjunction.

By correctly using the colon in the first choice, it effectively highlights the quotation, making it clear and impactful for the reader.