Explanation:

- Option 1: Helicobacter pylori

- ?? This is the correct answer. Helicobacter pylori is a bacterium that primarily causes peptic ulcers. It lives in the stomach lining and can lead to inflammation and ulcers.

- Option 2: Campylobacter

- While Campylobacter can cause gastrointestinal infections, it is not typically associated with peptic ulcers.

- Option 3: Bacillus cereus

- This bacterium is known for causing food poisoning, often linked to rice dishes, rather than ulcers.

- Option 4: Escherichia coli

- Commonly involved in intestinal infections, E. coli has no direct link to the formation of peptic ulcers.