The correct sequence of the various phases of a typical menstrual cycle is:
1. Menstrual → Follicular → secretory → Ovulatory
2. Menstrual → Follicular → Ovulatory → secretory
3. Ovulatory → Follicular → secretory → Menstrual
4. Menstrual → secretory → Follicular → Ovulatory
Which one of the following is the most likely reason of not occuring regular menstruation cycle in females ?
1. Fertilisation of the ovum
2. Maintainance of the hypertrophical endometrial lining
3. Maintainance of high concentration of sex-hormones in the blood stream
4. Retention of well-developed corpus luteuin