What is one of the ways in which sterility is ensured in single-dose vials? A. Any leftover medication in a vial must be discarded, not saved for later use. B. The contents of a vial should be drawn out and administered using a syringe only. C. All vials must be sterilized immediately after use to prevent any adherence of impurities. D. Vials are generally coated with an antibacterial film.