___A___ and ___B___ secrete their hormones when they receive orders from gland…

Concept: In the human endocrine system, some glands act as “master” regulators — they secrete tropic (hormone-controlling) hormones that travel through the bloodstream and direct other, subordinate glands to release their own hormones. A subordinate gland releases its hormone “on order” only after it receives the matching tropic hormone from its master gland.

1. Identify the master (order-giving) gland in this system: the pituitary gland, seated at the base of the brain, is the body's chief source of tropic hormones.

2. The pituitary secretes thyroid-stimulating hormone (TSH), which travels through the blood to the thyroid gland and triggers it to release thyroxine.

3. The pituitary also secretes adrenocorticotropic hormone (ACTH), which travels through the blood to the adrenal glands and triggers them to release corticosteroids.

4. Matching this to the stem's labels: the gland issuing the orders (C) is the pituitary, and the two glands that secrete hormones “on order” (A and B) are the thyroid and the adrenal glands.

Cross-check — the other offered triples do not fit this master-subordinate pattern:

• Pancreas, Adrenal glands, Thyroid: pancreatic insulin and glucagon release is driven by the blood-glucose level sensed by the pancreas itself, not by a signal sent from the thyroid gland, so the thyroid cannot be the order-giving gland here.

• Testes, Ovaries, Thyroid: the testes and the ovaries release their hormones on instruction from pituitary gonadotropins (LH and FSH), not from the thyroid, so the thyroid cannot be the order-giving gland here either.

• Pituitary, Pancreas, Thyroid: the pituitary is itself the order-giving gland rather than an order-receiving one, and pancreatic secretion is governed by blood-glucose feedback rather than by any signal from the thyroid.

Result: A = Thyroid, B = Adrenal glands, C = Pituitary, which matches the triple “Thyroid, Adrenal glands, Pituitary.”