Final answer:
Radio waves of sufficient frequency primarily pass through the ionosphere, which absorbs or reflects some types of radio waves while allowing others like FM and TV waves to travel with minimal interaction. The correct option is c).
Step-by-step explanation:
Radio waves of sufficient frequency primarily pass through the ionosphere. The ionosphere is a layer of charged particles that exists from about 48 kilometers (30 miles) to 965 kilometers (600 miles) above the Earth's surface. This layer absorbs or reflects AM radio waves, enabling them to travel long distances.
FM and TV waves, as well as other high-frequency radio waves, are not significantly absorbed by the ionosphere and thus can also travel through it effectively.
Other atmospheric layers, like the exosphere, are too high to have much interaction with radio waves intended for terrestrial communications. Therefore, the correct answer to which layer radio waves pass through is c) Ionosphere.