Final answer:
Oral contraceptives primarily prevent conception by blocking sperm from reaching the ovum.The correct option is A.
Step-by-step explanation:
Oral contraceptives primarily prevent conception by blocking sperm from reaching the ovum.
The pill contains the hormones estrogen and progestin, which cause changes in the lining of the uterus and the cervical mucus to keep the sperm from joining the egg.
By thickening the cervical mucus, oral contraceptives reduce the number of sperm that penetrate the cervix and reach the ovum. Changing the acidity of the vaginal canal is not the primary mechanism of action for oral contraceptives.The correct option is A.