Which of the following undergoes cyclical changes during the menstrual cycle to prepare the uterus for the implantation of an embryo? 

The endometrium undergoes cyclical changes during the menstrual cycle to prepare the uterus for the possible implantation of a fertilised egg.  The thickened lining provides a rich blood supply and nutrients for the growing embryo. If fertilisation does not occur, the endometrial lining is shed during menstruation, and a new cycle begins.