You are answering a USMLE-style medical question. Question: A 68-year-old woman presents with left lower quadrant pain that worsens with defecation. She describes the pain as 'crampy'. She also says she has suffered from mild constipation for the past few years. The patient denies any recent weight change or urinary symptoms. Her last menstrual period was 16 years ago. Her body temperature is 37.8°C (100.0°F), pulse is 102/min, respiratory rate is 16/min, and blood pressure is 133/87 mm Hg. On physical examination, tenderness to palpation in the left lower quadrant is present. The laboratory studies are presented as follows: Hemoglobin 13.2 mg/dL Hematocrit 48% Leukocyte count 16,000/mm³ Neutrophils 89% Bands 5% Eosinophils 0% Basophils 0% Lymphocytes 11% Monocytes 0% Platelet count 380,000/mm³ Which of the following is the most likely diagnosis in this patient? Options: A) Diverticulitis B) Hypothyroidism C) Adenocarcinoma of the colon D) Irritable bowel syndrome Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.