Which of the Following Is a Correct Statement About the Menstrual

Which of the following is a correct statement about the menstrual cycle?

A) Ovulation does not have to occur in every menstrual cycle,especially among girls during puberty and women in their forties.
B) The luteal phase of the menstrual cycle varies in length,especially among women in their thirties.
C) Irrespective of the duration of one's menstrual cycle,ovulation invariably occurs on day 14 from the start of menstruation.
D) The follicular phase of the menstrual cycle is the most constant,extending for 10 days from ovulation to menstruation.