Submitted by admin on Sat, 05/17/2014 - 20:47
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:
medium
toefl frequency:
2
toefl classification: