| A | B |
|---|
| plateau | a large, raised area of mostly level land |
| elevation | height of land above sea level |
| rift | a deep crack in Earth's surface |
| tributary | a river or stream that flows into a larger river |
| fertile | rich in the substances plants need to grow well |
| irrigate | to supply with water through a ditch, pipe, channel, or sprinkler |
| drought | a long period of little or no rain |
| oasis | a fertile place in a desert, with water and vegetation |
| savanna | a region of tall grasses with scattered trees |
| nomad | a person who has no permanent, settled home; moves from place to place |
| subsistence farming | raising just enough crops to support one's family |
| cash crop | a crop that is raised for sale |
| economy | a system for producing, distributing, consuming, and owning goods and services |
| diversify | to add variety to; increasing the variety of goods produced |
