In which layer of the atmosphere are the particles so far apart that they can travel hundreds of kilometers without colliding with each other? a. exosphere b. troposphere c. mesosphere d. thermosphere

Which of the following is not a challenge to instituting sound global environmental policies? a. most changes are inexpensive and easy to implement. b. elected leaders who support unpopular environmental issues often are not re-elected. c. economic considerations outweigh environmental ones in many societies. d. there is no way to enforce international environmental agreements.

Soil color only reflects the amount of organic matter present in soil.

What is the biggest country in south america?