You are answering a USMLE-style medical question. Question: An 80-year-old man is transferred from a step-down unit to a med-surg floor in the hospital. He had undergone a successful hernia surgery 14 hours ago. Before the surgery, he was pre-treated with atropine, scopolamine, and morphine and recovered well in the PACU after the surgery. There were no complications in the step-down unit and the patient continued to recover. On the med-surg floor, his temperature is 36.8°C (98.2°F), the heart rate is 98/min, the respiratory rate is 15/min, the blood pressure is 100/75 mm Hg, the oxygen saturation is 90%. On physical exam, he is a well-developed, obese man. His heart has a regular rate and rhythm and his lungs are clear to auscultation bilaterally. His incision site is clean, dry, and intact with an appropriate level of swelling and erythema. During the physical, the patient mentions some discomfort in his abdomen and pelvis and during a records review it is noted that he has not passed urine in the PACU, step-down unit, or since arriving on the med-surg floor. A bladder scan is inconclusive due to body habitus. What is the next best step in the treatment of this patient? Options: A) Insert a ‘straight cath’ into the patient’s bladder B) Aggressive IV fluids C) Digital rectal exam D) Renal ultrasound Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.