Menstruation occurs due to:A.  Regeneration of the endometrial liningB.  Declining levels of progesterone and estrogenC.  Rising levels of FSH and LHD.  Breakdown of the endometrial lining of the uterus

Breakdown of endometrial lining causes the menstrual discharge. This occurs because the declining levels of progesterone and oestrogens stimulate the release of prostaglandins that cause the uterine spiral arterioles to constrict. As a result, the cells of stratum functionalis become oxygen-deprived and start to die. Eventually, the entire stratum functionalis sloughs off.