Why does female body shed the lining of the uterus if an ovum is not fertilized?

If an ovum is not fertilized, the female body shed the lining of the uterus in a process called menstruation. Not releasing the non-fertilized egg will cause complications to the uterus of women. Think of it this way: Every month, the uterus readies the body for pregnancy through setting up a wall on the uterus where the fertilized egg is cradled and nourished. When ovum is not fertilized, the body will release the build-up in the lining through monthly menstruation to clear the uterus from possible infection.

Ithink your answer will be c let me know if it’s right

Generally travels west to east but often shifts to north and south