An outline is used to help the author organize ideas before writing.
Answer: The sentence that explains the purpose of an outline is: "An outline is used to help the author organize ideas before writing".
Explanation: An outline is a tool for the writer and not for the reader. The author uses it to organize the information that he/she will include in the piece of writing he/she is working on, such as an essay. However, the author only includes short phrases in the outline and not full sentences, and he/she arranges ideas in a particular order by using roman/arabic numbers or uppercase letters.
