Productivity is limited by in polar regions and by in the low-latitude tropics.

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.

Which movement developed in the early 1900s and encouraged the nationalist spirit of africans throughout the world? a. african nationalist b. tribalism c. pan-africanism d. african union

How does central place theory explain patterns in the size and distribution of cities?