When writing, you can most effectively use a dash
A. to add a formal touch to a sentence.
B. in place of an exclamation point.
C. to get the reader's attention.
D. in place of a semicolon
Personally, I would say that the correct answer is D) it is used instead of a semicolon. However, I saw all over the Internet that C might be the correct answer as well. I'd still go with D though.