Explanation: Usually the other options don't have a set time to write. Clustering is a type of prewriting taht allows a writer to explore many ideas as they occur to them. Like brainstorming or free associating, clustering allows writer to begin without clear ideas.
Free writing is a technique in which people are meant to write freely for a set period of time. This is usually done without worrying much about rhetorical concerns or conventions. Free writing is encouraged in order to initiate the writing process. It is also useful for overcoming writer's block and for developing new ideas for future texts.
