Answer:
D: To give the reader a variety of writing styles. There are lots of writing styles out there to help you. The author is describing what to do in one specific writing style and how to do it.
Step-by-step explanation:
If you separate the writing process into two stages, you can exploit these opposing muscles one at a time: first be loose and accepting as you do fast early writing; then be critically toughminded as you revise what you have produced.