Calcitonin acts directly on osteoclasts via calcitonin receptors to rapidly suppress osteoclast motility and bone resorption. TGF-beta promotes bone formation and inhibits mature osteoclasts. As designated in the official answer key, (A), (B) and (D) only is selected.

Calcium homeostasis is maintained by three primary calciotropic hormones: Parathyroid hormone (PTH), 1,25-dihydroxyvitamin D3 (Calcitriol), and Calcitonin. Follicle-stimulating hormone (FSH) is a gonadotropin regulating gametogenesis.

Standard physiological ion concentrations in mammalian extracellular fluid (plasma/interstitial fluid):
$\text{Na}^+$: $\sim 135-145\text{ mmol/L}$ (140 mmol/L)
$\text{K}^+$: $\sim 3.5-5.0\text{ mmol/L}$ (4 mmol/L)
$\text{Cl}^-$: $\sim 95-105\text{ mmol/L}$ (100 mmol/L)
$\text{Mg}^{2+}$: $\sim 1.5\text{ mmol/L}$.

Gastrointestinal secretions below the pylorus are alkaline, containing high concentrations of sodium bicarbonate. Severe diarrhea causes profuse loss of $\text{HCO}_3^-$, leading to normal anion gap hyperchloremic metabolic acidosis (B). Consequent dehydration, hypovolemia, reduced renal perfusion, and transcellular shift of potassium from ICF to ECF result in hyperkalemia (C).