Non-steroid peptide hormones enter the cell.

Correct Answer: B

Rationale: Peptide hormones do not enter cells; they act via surface receptors and second messengers.

Correct Answer: D

Rationale: Calcitonin lowers blood calcium by depositing it in bones, counteracting PTH.

Correct Answer: C

Rationale: Aldosterone acts on the kidney to regulate sodium and water reabsorption.

Correct Answer: A

Rationale: Type I diabetes may be triggered by viral infections in genetically susceptible individuals.

Correct Answer: B

Rationale: Hyperthyroidism increases metabolism and heat production; a cool environment helps manage heat intolerance.