Answer:
The display of dawn and the reflection of radio waves back to Earth result from the ionosphere.
Step-by-step explanation:
Ionosphere is one of the layers of the earth's atmosphere, characterized by containing charges of ions and electrons and covering between 60 km and 500 km altitude. The ionosphere - also known as thermosphere - is located between the mesosphere and the exosphere. This layer of the atmosphere is constantly ionized due to the radiation it receives from cosmic and solar rays. This layer is responsible for the display of dawn and the reflection of radio waves back to Earth.