Fertilization of the ovum Explanation for the correct option: Periodic vaginal bleeding, or menstruations, is a normal aspect of a woman's monthly cycle. Your body gets ready for pregnancy each month. A woman's egg and a man's sperm fuse during fertilization to create an embryo. Usually, the fallopian tube, which joins an ovary to the uterus, is where fertilization occurs. If the fertilized egg successfully travels via the fallopian tube and implants in the uterus, an embryo begins to develop. Explanation for the incorrect options: Option B: The corpus luteum creates from an ovarian follicle during the luteal period of the monthly cycle or estrous cycle. Option C: Menstruation can begin or end depending on the blood levels of oestrogen and progesterone. High levels of sex hormones interfere with ovulation, implantation, and alter the cervical mucus' quality, which delays or hinders sperm entry. Option D: Endometrial hyperplasia has an impact on the female reproductive system. The endometrium, the lining of the uterus, develops improperly when there are too many cells (hyperplasia). Final Answer: The most likely root cause why menstruation is not taking place in regularly cycling human females is the fertilization of the ovum.