Answer
a. a lack of ovarian follicles that are able to ovulate.
Work Step by Step
Menopause occurs when the ovaries run out of functional follicles capable of responding to hormones and producing estrogen and progesterone.
As the follicle pool is depleted, ovulation ceases, and estrogen levels drop.
The pituitary gland actually increases secretion of FSH and LH, but the ovaries can no longer respond effectively because there are few or no follicles left.
So, while the ovaries do become less responsive (option c sounds close), the primary cause is the loss of follicles, which is what triggers the unresponsiveness — making (a) the best answer.
