A 75-year-old woman presents with heartburn and dyspepsia. She was diagnosed with osteoarthritis 4 years ago. For the past 18 months, she has been managing pain with naproxen. The gastroenterologist suggests that the patient be tested for Helicobacter pylori infection. What is the most sensitive and specific non-invasive method to diagnose this infection? A. Gastric biopsy B. Fecal antigen test C. Urea breath test D. Culture of H. pylori