Answer c is correct. The recommended primary therapy for H. pylori infection includes a PPI, clarithromycin, and amoxicillin (clarithromycin-based triple therapy).

Answer a is incorrect. Levofloxacin-based triple therapy has been used outside the United States, but typically it is used as salvage therapy after failing one or more H. pylori regimens. Additionally, levofloxacin is a broad-spectrum antibiotic compared to clarithromycin. If possible, a narrow-spectrum antibiotic should be utilized over a broad-spectrum antibiotic.

Answer b is incorrect. The regimen of PPI, metronidazole, and clarithromycin should be reserved for patients with a penicillin allergy or those patients unable to tolerate bismuth quadruple therapy.

Answer d is incorrect. The regimen of PPI, bismuth, metronidazole, and tetracycline (bismuth quadruple therapy) is used as salvage therapy.