| A | B |
|---|
| nuclear fusion | the combining of lightweight atomic nuclei to form a heavier nucleus |
| passive solar heating | heating a home with south-facing windows and thick stone walls |
| biomass | wood, solid waste, or crops used to produce energy |
| coal | energy source from the remains of organisms that lived millions of years ago |
| hydroelectricity | energy generated by falling water |
| ethanol | gasoline alternative that can be made from agricultural products |
| hydrogen | clean-burning |
| active solar heating | uses solar collectors to trap the sun's energy |
| wind | inexhaustible energy source |
| nuclear fission | the breaking of bonds holding together subatomic particles |
