B. Asking how you’ll achieve the purpose is the correct answer.
Explanation:
Letter A is one of the strategies because by considering the purpose the writer can help himself clarify the intention of the text.
Letter C is also correct because a draft can be helpful to categorize and discard information.
Letter D is also part of the strategies because by starting the ideas flowing, the writer can understand which ones are helpful to achieve his purpose.
Asking how you'll achieve the purpose is not part of the strategies because instead of helping the writer, it might change his perspective and the purpose.
So that way you can accomplish certain parts of what you need to focus on and how to improve it becomes easier that way and make it much more easy to remember
