You are answering a USMLE-style medical question. Question: A 24-year-old woman is brought to the physician because of agitation, confusion, and lethargy. She has also had progressive recurring headaches and visual impairment over the last month. Three days ago, she had a seizure but has not seen a physician. She is oriented only to person. Her temperature is 36.7°C (98.1°F), pulse is 90/min, and blood pressure is 110/80 mm Hg. Capillary refill time is more than 3 seconds. Her laboratory studies show: Hemoglobin 11.2 g/dL Leukocyte count 7000/mm3 Serum Na+ 148 mEq/L Cl- 100 mEq/L K+ 3.8 mEq/L HCO3- 26 mEq/L Urea nitrogen 18 mg/L Glucose 90 mg/L Creatinine 0.8 mg/L Osmolality 300 mOsmol/kg H2O Urine osmolality 240 mOsm/kg H2O Which of the following is the most likely explanation for this patient's hypernatremia?" Options: A) Increased water intake B) Increased adrenocorticotropin hormone secretion C) Decreased antidiuretic hormone secretion D) Decreased adrenocorticotropin hormone secretion Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.