The correct answer is C. Ductless gland.
Endocrine glands are ductless glands that secrete hormones directly into the bloodstream. These hormones then travel to target cells throughout the body, where they regulate a variety of physiological processes, including metabolism, growth and development, tissue function, sexual function, reproduction, sleep, mood, and behavior.
Micro glands are glands that are too small to be seen with the naked eye. Macro glands are glands that are large enough to be seen with the naked eye. Acidic glands are glands that secrete an acidic substance.
Endocrine glands are not micro glands, macro glands, or acidic glands. They are ductless glands that secrete hormones directly into the bloodstream.