Answer: c. keep the focus of the specific form you have in mind.
The other items mentioned are done in other parts of the process.
Exploring and narrowing your topic and gathering details -- these happen during the research phase.
Doing the actual writing (including keeping the focus of the specific form you have in mind) happens in the drafting phase, as you write a draft of your paper.
Revise your work for clarity and word choice as well as checking your work for grammar, spelling, and punctuation -- these are parts of the final revision process.
