You are answering a USMLE-style medical question. Question: Six days after undergoing surgical repair of a hip fracture, a previously healthy 79-year-old woman is agitated and confused. She is unarousable during the day, but then is awake and impulsive during the night, requiring frequent reorientation. Her husband says that she usually drinks one to two glasses of wine weekly. Her only current medication is oxycodone for pain. Her vital signs are within normal limits. She is distressed and oriented to person but not to place or time. Neurologic examination shows inattentiveness but no focal deficits. Urine dipstick is normal. Which of the following is the most likely cause of her current condition? Options: A) Dementia B) Opioid intoxication C) Delirium D) Urinary tract infection Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.