A. Increasing antidiuretic hormone secretion: Dehydration increases plasma osmolality, which stimulates the posterior pituitary to release ADH. ADH increases water reabsorption in the collecting ducts, conserving water and producing concentrated urine. B. Increasing sodium excretion: During dehydration, the body conserves sodium (via aldosterone) to help retain water, not excrete it. C. Increasing urine production: Dehydration leads to decreased urine output, not increased, to prevent further fluid loss. D. Decreasing renin secretion: Dehydration increases renin secretion, activating the RAAS system to conserve sodium and water.