Most Birth-Control Pills Contain Both Progestin (Biologically Similar to Progesterone)

Most birth-control pills contain both progestin (biologically similar to progesterone) and estrogen. By taking a pill over consecutive days the amount of each hormone is maintained at a constant concentration in the circulating blood, inhibiting ovulation. Based on this information, what is the MOST likely mechanism for how birth-control pills affect ovulation?

A) They inhibit growth of the uterine lining so implantation cannot occur.
B) They inhibit growth of follicles so that immature eggs will be released.
C) They inhibit maintenance of the corpus luteum after ovulation.
D) They inhibit the release of the egg so that ovulation does not occur.