During the prewriting stage, an author will determine all of the following except a. purpose. b. audience. c. examples. d. medium.

During the prewriting stage of any literature, what would you worry about? Well, you want to portray to a certain audience (Don't wanna be writing a 50 chapter horror story for a kindergarten class), so B is out of the question.

If you're writing, you obviously have a purpose to get across, it's part of the foundation of a rough draft. So there goes A.

But, if it's an essay, yes you do need to get a couple of examples. I'm going to assume that the question is regarding an essay, so C can go now.

And All that leaves is D. Now I'm not 100% sure if a medium is something you HAVE to worry about in prewriting, but I don't really worry much about it.

I'll say 'D' is the one you don't need to worry about.