The correct answer is B. Endocrinology.
Endocrinology is the study of the endocrine system, which is a system of glands that produce hormones that regulate many important body functions, such as growth, metabolism, and reproduction. Ductless glands are glands that do not have ducts, and they release their hormones directly into the bloodstream. Some examples of ductless glands include the pituitary gland, the thyroid gland, and the adrenal glands.
Embryology is the study of the development of an embryo from conception to birth. Ecology is the study of the relationship between organisms and their environment. Euthenics is the science of improving human health and well-being through environmental factors.