The question says,'menstruation does not occur if the ............ The correct option is D. The uterine lining usually build up in order to serve as a bed and support for fertilized a egg. If fertilization does not occur, the uterine lining breaks down and come out as menstruation, but if fertilization occurs, then the uterine lining will not break down but will support the fertilized egg all through the pregnancy period.
