*Question E3B13:
What type of polarization is supported by ground-wave propagation?*  

*Correct Answer is  A: Vertical*  

### AI Response: (may contain errors)  

Ground-wave propagation is a mode of radio wave propagation that follows the contour of the Earth. It is most effective at low frequencies, such as those used in the AM broadcast band and lower HF bands.

### Explanation:

1. **Correct Answer: Vertical**
   - **Vertical Polarization**: Ground-wave propagation is best supported by vertically polarized waves. This is because vertically polarized waves can more effectively follow the Earth's surface, minimizing losses due to the ground's conductivity and dielectric properties. The electric field of a vertically polarized wave is perpendicular to the ground, which helps maintain the wave's strength over longer distances.

2. **Why Other Choices Are Incorrect:**
   - **Horizontal Polarization**: Horizontally polarized waves are less effective for ground-wave propagation because the electric field is parallel to the ground. This orientation leads to higher attenuation due to ground absorption and reflection, reducing the effective range.
   - **Circular Polarization**: Circularly polarized waves are a combination of vertical and horizontal components. While they can be used in some applications, they are not optimal for ground-wave propagation due to the horizontal component's inefficiency in this mode.
   - **Elliptical Polarization**: Similar to circular polarization, elliptical polarization includes both vertical and horizontal components. The horizontal component again leads to increased attenuation, making it less suitable for ground-wave propagation.

### Key Points:
- Ground-wave propagation is most effective with vertical polarization.
- Horizontal and mixed polarizations (circular and elliptical) suffer from higher attenuation when interacting with the ground. 

Understanding these principles helps in selecting the appropriate antenna polarization for effective ground-wave communication.