Why does the level of fsh decrease and remain at a relatively low level during days 15-28 of the cycle?

The FSH will decrease and remain at a low level during the 15-28 days of the cycle because at this stage, the egg is waiting to be fertilized. The FSH needs to be low to prepare the uterus lining in case the egg will be fertilized.

the glands which are associated with each description is given below:

pancreas - is an endocrine and exocrine gland that secretes juices with enzymes for digestion. salivary glands- with protection and digestion in the mouth. liver- secretes bile for digestion.   lachrymal glands - secrete tears to moisten eyes and protect them from particles and infection.   sweat gland -regulates water, salt, and temperature. oil glands - to form a protective barrier on the skin.   goblet cells - secrete mucus for protection.