I don't know what high school you went to but where I went many students were able to graduate with D's in Junior High and Senior High (post-secondary as you say).
Post-secondary usually implies University/College, "secondary" being your "Senior High". My comment regarding the C's is related to the Univ I went to for my EE degree.
BOy, now I feel so stupid. I guess I might as well go for stupiter since when I google EE I can't figure out what it is. What is EE?