C. The particles that make up the aluminium bar are moving faster.
Explanation:
You can notice how you rub your hands outside during winter, right? It gets warmer the more you rub your hands, so it is basically like that, but with the particles of the aluminium bar.
These are things that won't be going away. Natural gasses and fossil fuels will likely run out someday or become much harder to find. When you use these sources of energy, they won't be going away and therefore will be sustainable because we can always continue using them.
