Why does the level of follicle-stimulating hormone decrease and remain at a relatively low level during the luteal phase of the cycle?

During the luteal phase or the latter part of the menstrual cycle, FSH or follicle stimulating hormone decreases or remained at the low level because it is suppressed by the high levels of estrogen and progesterone. FSH together with lutienizing hormone LH are hormones needed in the growth, maturity and release of ovarian follicles in the ovary.

Secretion of glucagon causes  an increase in the concentration of blood glucose

Secretion of a decrease in the concentration of blood glucose.

Explanation:

So the answer is A). a decrease in the concentration of blood glucose.