It’s repetition- this is effective as it not only promotes clarity, but encourages the acceptance of an idea. It also gets stuck in the readers’ head, so they can remember clearly what the text is about, and the theme. Hope this helps!
Wood: Combustion reaction converts chemical energy into light and heat. Petroleum: Can be burned to release light and heat or changed into another form of chemical energy, such as gasoline. Chemical batteries: Store chemical energy to be changed into electricity.
