The correct answer is A. Nuclear fission.
Nuclear fission is the process of splitting a large atomic nucleus into two or more smaller nuclei. This process releases a large amount of energy, which can be used to generate electricity. Nuclear fission is the process that is used in nuclear reactors.
Nuclear fusion is the process of combining two or more small atomic nuclei into a larger nucleus. This process also releases a large amount of energy, but it is much more difficult to achieve than nuclear fission. Nuclear fusion is the process that powers the sun and other stars.
Cold fusion is a hypothetical process in which nuclear fusion occurs at room temperature. This process has never been conclusively demonstrated, and it is generally considered to be a pseudoscience.
Superconductivity is a phenomenon in which certain materials lose all electrical resistance when they are cooled to very low temperatures. Superconductivity can be used to create powerful magnets and to transmit electricity with very little loss.
I hope this helps!