The correct option is D all of these
Menstruation is the discharge of blood along with the mucosal tissues due to the shedding of endometrial lining of the uterus. This is called the menstrual/bleeding phase of the menstrual cycle.
During pregnancy, all the events of menstrual cycle stop and hence there is no menstruation.
However, stress and poor health can also be responsible for the absence of menstrual cycle.