as far as I understand (keeping in mind that I am a first time applicant), it varies from school to school. Some say right on their website that they require a 2.0 (C) to accept a pre-req. At my undergrad school, most of the pre-reqs for vet school were also required for my BS. So you'd have to retake a D anyway if you wanted your BS. Again, I know it varies from school to school (some schools are probably more understanding than others!). guarenteed someone else on here has a better answer, but I figured I'd give my $0.02. Good luck.