Select the STD caused by bacteria among the following.

Options

A. Genital herpes
B. Syphilis
C. Hepatitis-B
D. Giardiasis

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks to identify which sexually transmitted disease (STD) is caused by bacteria from the given options.

2. **Defining STD**: An STD (sexually transmitted disease) is an infection that is primarily spread through sexual contact.

3. **Reviewing Options**: The options provided are:
- Genital herpes
- Syphilis
- Hepatitis B
- Gardiasis

4. **Analyzing Each Option**:
- **Genital Herpes**: This is caused by the herpes simplex virus, so it is viral.
- **Syphilis**: This is caused by the bacterium Treponema pallidum, making it a bacterial STD.
- **Hepatitis B**: This is caused by the hepatitis B virus, so it is also viral.
- **Gardiasis**: This is caused by the protozoan Giardia lamblia, making it a protozoan infection.

5. **Identifying the Correct Answer**: Among the options, syphilis is the only STD that is caused by bacteria.

6. **Conclusion**: Therefore, the STD caused by bacteria is **syphilis**.