what are hormones?\no glands\no cells\no chemical messengers\no building blocks of proteins

Brief Explanations:

Hormones are chemical messengers produced by glands and secreted into the bloodstream to regulate various physiological processes. Glands are the organs that produce hormones, cells are the basic unit of life and not what hormones are defined as, and building - blocks of proteins are amino acids.

Answer:

C. chemical messengers