Many cases of gastric ulcer or gastritis are caused by the presence of the bacterium:

A. Ebola
B. Helicobacter pylori
C. Candida albicans
D. Escherichia coli

b
Rationale: Helicobacter pylori is a bacterium responsible for many cases of gastric ulcer or gastritis. Infection is usually treated successfully by using a combination of antibacterials.