ionosphere

definition: 
The layer of the earth’s atmosphere which contains a high concentration of ions and free electrons and is able to reflect radio waves. It lies above the mesosphere and extends from about 80 to 1,000 km above the earth’s surface.
sentence: 
The ionosphere reflects neither FM radio nor broadcast television, itself a part of the radio spectrum.
difficulty: 
medium
toefl frequency: 
1
toefl classification: