| A | B |
|---|
| Empire | A large area of different groups of people controlled by one ruler or government. |
| Irrigation | A method by which water is brought into dry areas. |
| Specialize | People who spend most of their time doing one kind of job. |
| Civilization | A culture that has developed complex systems of government,education, and religion. |
| Ice Ages | The time when Earth went through periods of extreme cold. |
| Glaciers | Earth's water frozen into huge sheets of ice. |
| Slavery | A practice of owning people and forcing them to work. |
