A red blood cell contains a large nucleus; it is thicker near the center and thin around the rim of the cell:

Innate defenses counter specific disease-causing agents, whereas adaptive defenses include mechanical and chemical barriers.

Choice A is wrong because it confuses the two types of defenses.

Innate defenses are nonspecific and include physical barriers such as the skin, molecules that are toxic to invaders, and phagocytic cells that ingest invaders.

Adaptive defenses are specific and are activated by the innate immune system.

They involve the production of antibodies and specialized cells that recognize and eliminate specific pathogens.

Normal ranges are not applicable in this question as it is about the definitions of innate and adaptive defenses.

The thyroid gland secretes triiodothyronine (T3), which is one of the two main thyroid hormones that affect almost every physiological process in the body.

T3 is the more metabolically active hormone produced from thyroxine (T4), which is the other thyroid hormone.
Choice A is wrong because the adrenal gland secretes hormones such as cortisol, adrenaline, and aldosterone, which are involved in stress response, blood pressure regulation, and metabolism.
Choice B is wrong because the pancreas secretes hormones such as insulin, glucagon, and somatostatin, which are involved in blood glucose regulation and digestion.
Choice D is wrong because the parathyroid gland secretes parathyroid hormone (PTH), which is involved in calcium and phosphate homeostasis.

Normal ranges for T3 levels vary depending on the laboratory and the method of testing, but they are usually between 100 and 200 nanograms per deciliter (ng/dL) for total T3 and between 2.3 and 4.2 picograms per milliliter (pg/mL) for free T.