Widal test is to diagnose tuberculosis/typhoid.

Explanation

### Step-by-Step Solution:

1. **Understanding the Widal Test**: The Widal test is a serological test used to diagnose typhoid fever. It detects the presence of specific antibodies in the blood against the bacteria Salmonella typhi.

2. **Identifying the Diseases**: The question presents two diseases: tuberculosis and typhoid fever. It is important to know which disease the Widal test is associated with.

3. **Bacterial Diseases**: Both tuberculosis and typhoid fever are bacterial diseases. Tuberculosis is caused by Mycobacterium tuberculosis, while typhoid fever is caused by Salmonella typhi.

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