stratosphere

definition: 
The layer of the earth’s atmosphere above the troposphere, extending to about 32 miles (50 km) above the earth’s surface (the lower boundary of the mesosphere).
sentence: 
The stratosphere extends above the troposphere to about 150,000 feet and is the region where the ozone layer is formed.
difficulty: 
easy
toefl frequency: 
2
toefl classification: