Question

Which causes a drop in female hormone levels?
the onset of the menstrual flow
the release of an egg from the ovary
the thickening of the uterine wall
the failure of an egg to be fertilized

Answer 1

The failure of an egg to be fertilized.

Explanation: If the egg is not fertilized, the corpus luteum breaks down, causing progesterone and estrogen levels to fall. That hormone drop triggers the onset of menstruation (the uterine lining shedding).