The correct option is A Prevents ovulation
Oral administration of the small doses of either progestogens or progestogen-oestrogen combinations is one of the contraceptive method used by the females. They are used in the form of tablets and hence, are popularly called the pills. Pills have to be taken daily for a period of 21 days, starting preferably within the first five days of menstrual cycle. After a gap of 7 days (during which menstruation occurs) it has to be repeated in the same pattern till the female desires to prevent conception. They inhibit ovulation and implantation as well as alter the quality of cervical mucous to prevent/retard entry of sperms. Pills are very effective with lesser side effects and are well accepted by the females.