Menstruation is triggered by

A) reduced secretion of estradiol and progesterone from the corpus luteum.
B) a surge of androgens from the adrenal cortex.
C) implantation of a fertilized ovum in the uterus.
D) a surge of estrogens from the adrenal cortex.
E) increased secretion of estrogen and progesterone from the corpus luteum.

Answer: A