Answer:
Non-renewable resources (energy).
Step-by-step explanation:
Renewable energy is also known as clean energy and it can be defined as a type of energy that are generated through natural sources or technology-based processes that are replenished constantly. Some examples of these natural sources are water (hydropower), wind (wind energy), sun (solar power), geothermal, biomass, waves etc.
Basically, a renewable energy source is sustainable and as such can not be exhausted.
On the other hand, a non-renewable energy refers to an energy source such as fossil fuels that takes a very long time to be created or their creation happened long ago and isn't likely to happen again e.g uranium. Fossil fuels, such as coal, oil, and natural gas, come from deep inside the Earth where they formed over millions of years ago.
Hence, it is very important to conserve fossil fuels because they are non-renewable resources (energy), unstainable and can be exhausted.