It's needed to produce energy (4)
I believe the answer is:
fuel
(Other definitions for fuel that I've seen before include "Material for burning" , "Material fed to flames" , "Combustible material" , "Combustibles" , "Burned source of energy" .)
I believe the answer is:
fuel
(Other definitions for fuel that I've seen before include "Material for burning" , "Material fed to flames" , "Combustible material" , "Combustibles" , "Burned source of energy" .)