This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oncology, Subject name: Medicine
A 62-year-old man presents to the emergency department with a 1-day history of dark tarry stools and light-headedness. He also reports a 1-month history of intermittent abdominal discomfort and poor appetite. For the pain he takes ibuprofen on an as needed basis.On physical examination, the blood pressure is 102/75mm Hg, heart rate is 110/min, and the abdomen is soft and nontender. He undergoes urgent upper endoscopy that finds an ulcerating lesion in his stomach and biopsies confirm gastric cancer. Which of the following is a risk factor for carcinoma of the stomach? 
Select and explain. 
A. Helicobacter pylori infection, B. high socioeconomic status, C. high-protein diet, D. high alcohol consumption
A: Helicobacter pylori infection
Answer: A: Helicobacter pylori infection 
Explanation: H pylori is another important risk factor, since it causes gastritis that eventually leads to chronic atrophic gastritis, metaplasia, dysplasia, and then carcinoma. Low dietary vitamin C, and high salt and nitrate consumption predispose to gastric cancer, as does ingestion of smoked foods. Smoking is a risk factor, but alcohol is not.