One of the First Indications That a Woman Is Pregnant

One of the first indications that a woman is pregnant is that she misses her monthly menstrual period.This is the result of

A) hormones secreted by the zygote following fertilization.
B) the arrival of the blastocyst in the uterus.
C) the secretion of luteinizing hormone (LH) by the corpus luteum once the embryo implants.
D) the secretion of human chorionic gonadotropin (hCG) by the blastocyst once it implants.
E) the maintenance of the corpus luteum by estrogen and progesterone secreted by the embryo once it implants.