What classes do you have C's in? If it's in a science pre-req strongly consider retaking it, if it's in the economics, calculus, physics courses I wouldn't worry too much about those.
If the classes you have D's in are outside of the pre-reqs don't worry about 'em. **** happens and those likely won't be counted against you. But, if they are in pre-reqs you HAVE to retake them. All professional schools require a C- or higher for the pre reqs.