Which of the following statement(s) is/are true for menstrual cycle?

(i) It occurs in female of all mammals.

(ii) In human non-pregnant normal females, ovulation is repeated at an average interval of about 28/29 days.

(iii) In human beings, ovulation cycles ceases around 50 years of age; that is termed as menopause.

(iv) Lack of menstruation is always an indicator of pregnancy.

(v) Menstruation only occurs if the released ovum is fertilized.

(vi) Menarche may also be due to stress, poor health.