Answer:
B. Anytime they want to develop more ideas
Step-by-step explanation:
I say this because you don't have to have any ideas(a), you can free-write and get something down, and this also takes out (c) because you can free-write, and while prewriting you can make up topics, plots, settings, characters, etc. and brainstorming random things to incorporate into your writing because prewriting is what you do before anything else. It's like finding the equation in math word problems. You have to find the equation in order to find the answer.