Which one term in each of the following includes the other three?

(a) thyroid, ductless gland, thymus, pituitary, ovary

(b) adrenalin, insulin, hormone, thyroxine, estrogen

(a) Thyroid, pituitary, thymus, and ovary are types of ductless glands.

Endocrine glands are also known as the ductless glands because of the fact that their secretions are released directly into the blood, not to any tubes or ducts. Hypothalamus, Pituitary gland, Pineal body, Thyroid, Parathyroid, Adrenal glands, Pancreas, and Gonads are the major glands that make up the human endocrine system.

(b) Adrenalin, insulin, thyroxine, and estrogen are types of hormones.

Hormones are chemicals synthesized and produced by the specialized glands to control and regulate the activity of certain cells and organs. These specialized glands are known as endocrine glands.