does not act on its target cell by binding with a G-protein coupled receptor.

Correct Answer: C

Rationale: Thyroid hormone acts via intracellular nuclear receptors, not G-protein receptors.

Correct Answer: C

Rationale: Insulin and somatostatin both inhibit glucagon release from A cells. Insulin has disulfide bonds, somatostatin does not; only insulin causes K^+ uptake.

Correct Answer: D

Rationale: Cholesterol inhibits HMG-CoA reductase, is esterified by ACAT, and downregulates LDL receptors via SREBP, making all statements true.

Correct Answer: C

Rationale: Glucose uses Na^+-dependent SGLT1 for luminal uptake; fructose uses GLUT5 (Na^+-independent). Absorption is mainly in the jejunum.

Correct Answer: D

Rationale: Osteoclasts originate from monocyte/macrophage lineage in bone marrow.