Explanation:

- Option 1: Typhoid fever

- The Widal test is commonly used to diagnose typhoid fever.

- It detects antibodies against Salmonella bacteria, which cause the disease.

- Correct Answer

- Option 2: Tuberculosis

- This is caused by Mycobacterium tuberculosis.

- The Mantoux test or sputum test is typically used for diagnosis, not the Widal test.

- Option 3: Cancer

- Cancer is a complex group of diseases with no singular diagnostic test like the Widal.

- Option 4: AIDS

- Caused by HIV, diagnosed typically through ELISA, not the Widal test.