The optimal time and temperature required for sterilization in an autoclave is___________________?

A. 140°C x 2 hrs. x 10 lbs pr.
B. 121°F x 15 mts. x 15 lbs pr.
C. 121°F x 15 sec. x 15 lbs pr.
D. 121°C 15 mts. x 15 lbs pr.