C. to organize evidence before writing
The outline is an optional but necessary step in the easy-writing process as it helps us to see the big picture of our paper and decide how to approach the main subject and how to arrange our ideas.
In the making of an argumentative essay, an outline will help us to determine which points we want to approach, how do they relate to each other, whether or not we have sufficient evidence to support each of the points and it will help us to organize all the ideas and evidence before writing.