Final answer:
The correct option for the given question is 'd. centuries, millennia', indicating that the remaining oil and natural gas reserves are expected to last approximately decades, while coal reserves could last for millennia based on current data.
Step-by-step explanation:
The question posed regards the estimated time scale for the exhaustion of fossil fuels such as oil, natural gas, and coal. To fill in the blanks, the correct option based on current estimates is: The oil and natural gas that remains will last on the scale of decades, and the coal will last on the scale of millennia.
Current estimates suggest that known reserves of petroleum will be exhausted in about 60 years, while supplies of natural gas are estimated to run out in about 120 years. With coal being relatively abundant, comprising over 90% of the world's fossil fuel reserves, and more difficult to mine and ship, its estimated time scale for exhaustion is much longer, potentially lasting on the order of millennia.
This assessment is based on an understanding that fossil fuels, including oil, natural gas, and coal, have a finite supply. While fossil fuels will likely be exhausted in a few generations, coal will persist longer due to its greater abundance relative to oil and gas. Carefully considering the consumption rates and proven reserves, as well as the history of usage and growth patterns regarding fossil fuels, we can conclude that option 'd. centuries, millennia' is the most accurate choice for filling in the blanks.