Explanation:

Nuclear fission is the process where a heavy atomic nucleus splits into two or more lighter nuclei, releasing a tremendous amount of energy. This process is harnessed in Nuclear reactors (Option D) to generate electricity and is the principle behind the destructive power of an Atom bomb (Option D). The Sun (Options A, B, C) generates energy through nuclear fusion, where light nuclei combine to form heavier ones. A Hydrogen bomb (Option A) also primarily uses nuclear fusion, triggered by a fission reaction.