| A | B |
|---|
| plateau | large raised areas of mostly level land |
| elevation | the height of land above sea level |
| escarpment | steep cliff |
| cataracts | rock-filled rapids |
| silt | tiny bits of rocks and dirt that build up on the bottoms of rivers and lakes |
| fertile | containing substances that plants need in order to grow well |
| tributaries | small rivers and streams that flow into a larger river |
| irrigate | to artificially water |
| oasis | a place where springs and fresh underground water make it possible to support life in a region that gets little rain |
| savanna | a region of tall grasses |
| nomads | people who move around to various places to make a living |
| subsistence farming | to raise crops to support their families and animals |
| cash crop | a crop that is raised for sale |
| economy | a system for producing, distributing, consuming, and owning goods, services, and wealth |
| diversify | to add variety |
