The value of prewriting is that it
a. provides the writer with the basic ideas for the writing of the paper.
b. organizes the writer's topic into a readable format.
c. guarantees the writer that the other stages will not have to be revisited.
d. allows the writer to check spelling and punctuation before progressing too far into the piece of writing.

The value of prewriting is that it a. provides the writer with the basic ideas for the writing of the paper.

Explanation:

The first step in the writing process is prewriting, where the writer finds an idea, writes it down and starts clarifying his or her thoughts. Therefore, prewriting stage is the step where a writer thinks about the basic ideas for the writing of the paper, usually followed by drafting, revision, edition and publishing.