Because all those energy sources are natural and will always be there, when ever there is a need for extra energy.
Are you looking for the term for a chemical pollutant?
Answer:
The needed options are
A. an uncontrolled experiment
B. intuitive reasoning
C. extrapolation
D. replication
E. exploration
The ANSWER is D. replication
Explanation:
Replication in research means using the same method and methodology in proximity to the original research work.
It helps in bringing, validating and proving the original study is up-to-date. It may be done using the same exact methods in a different cultural settings, location or different research subjects to determine if the original experimental results is up-to-date.