Solution:

Menstruation is the natural bleeding of the vaginal line that begins around adolescence and continues until menopause. During this time, the body begins to prepare for pregnancy.

Every month, an egg is released from one of the ovaries, and the uterus prepares itself for the fertilized egg. The inner lining of the uterus thickens and the embryo receives enough blood. Fertilization of the egg does not occur because there is no interaction between the egg and the sperms. When an egg is not fertilized, the uterine lining gradually breaks down, resulting in menstruation.