A C is a passing grade, right? I was in hospitals and rehab a lot during high school, one year I missed over 700 hours (of the approx 1050 school hours in a year) and I passed the year with C's and low B's by doing a lot of homework.. and next year I barely attended school and had no time to do homework and I had to repeat the year. There's no shame in failing because of a "higher power" (in this case, your surgery and rehab) interfered. It's commendable that you're passing the year - even if it's "only" with a C - despite everything.