Once you acquire these two basic skills, you'll be able to transform a vague idea in your mind into a coherent piece of writing.
a. doing research and organizing your ideas
b. describing people and writing conversation
c. doing interviews and browsing through books
d. using the internet and the on-line catalog

  In this sentence: Once you acquire these two basic skills, you'll be able to transform a vague idea in your mind into a coherent piece of writing. It is letter A. Doing research and organizing your ideas which is very relatable when one is making an outline.  

The purpose of an outline is to organize your thoughts, guide you through your paper to works cited, make sure that you do not plagiarize and help visualize your information. All the choices above are the purposes of an outline. It organizes your thoughts as it gives you the guide on foreseeing the possible subtopics. It helps you visualize the information while you are brainstorming the possible topics related to your theme. It will help you from plagiarizing because you could cite sources instead.