The correct answer is option 'C': Ionosphere reflects waves in these bands.

Explanation:

Radio waves are a type of electromagnetic radiation that can be used for long-distance communication. They are transmitted from a transmitter and received by a receiver. However, the Earth's atmosphere can affect the transmission and reception of these waves.

When it comes to long-distance radio broadcasts, short-wave bands are commonly used. There are several reasons for this, but one of the main reasons is the ability of the ionosphere to reflect these waves.

The ionosphere is a region of the Earth's upper atmosphere that is ionized by solar radiation. It is composed of several layers, each with different properties. One of these layers, known as the F layer, is particularly important for long-distance radio communication.

When radio waves in the short-wave band are transmitted upwards towards the ionosphere, they encounter the F layer. This layer contains a high concentration of ions, which allows it to reflect these waves back towards the Earth's surface. This reflection allows the waves to travel over long distances, as they are essentially bouncing off the ionosphere and back down to the Earth.

Other layers in the ionosphere, such as the D and E layers, can also contribute to the reflection of radio waves, but the F layer is particularly effective for short-wave bands. This is because the F layer is located at a higher altitude compared to the other layers, allowing for a greater reflection of the waves.

In addition to the reflection of radio waves, the ionosphere also affects their propagation. The ionized particles in the ionosphere can cause the waves to refract or bend, which can lead to phenomena such as skywave propagation. Skywave propagation allows radio waves to be received beyond the line of sight, making it possible for long-distance communication.

In conclusion, long-distance radio broadcasts use short-wave bands because the ionosphere, specifically the F layer, reflects waves in these bands. The ionosphere's ability to reflect and refract radio waves allows for long-distance communication, making it an essential part of long-distance radio broadcasting.