The correct answer of the given question above would be the third option. What the main idea does not do is to show what a reader will learn, rather, it only shows what the story is about, summarizes the details and events, and illustrates an important idea. Hope this answers your question.
Johanna told John she had finished the book she was writing last time they met.
She said she finished it last week.
She told him she has started another one now.
She told him she is writing a love story and will finish it soon.
She told him she writes a little everyday.
The correct answer should be locate basic information.
When you are doing the preliminary research, you are just reading through a bunch of sources and information that you may or may not use while writing. You still aren't deciding which exact sources you are actually going to use, but rather just trying to find them and later on make that decision during another stage of writing.