| A | B |
|---|
| Necessary for a prediction | Observations made over a long period of time. |
| Cyclic data predicts this | Future changes in the environment |
| Earth and Moon's phases | cyclic and predictable |
| interface | A boundary between two regions of change |
| change | When the properties of a system are altered |
| Solar | This energy source is most nearly pollution free. |
| Natural processes | The least likely source of atmospheric pollution in cities. |
| Frame of Reference | A basis for comparison |
| Environmental Equilibrium | Balance of changes within the environment. |
