The correct option is C Preventing ovulation
Oral administration of small doses of either progestin or progestin–estrogen combinations is another contraceptive method used by the females.They inhibit ovulation and implantation as well as alter the quality of cervical mucus to prevent/retard entry of sperms. Pills are very effective with lesser side effects and are well accepted by the females.
So, the correct option is- prevent ovulation.