NUCLEAR FUSION is the combining of two lighter atomic nuclei to form a new heavier nuclei. Energy is produced and mass is lost in this process. The sun is an excellent example of NUCLEAR FUSION as it generates energy by fusing two heavy hydrogen atoms into a helium and a neutron.
Therefore the correct response would be D. All of these
NUCLEAR FUSION is not to be confused with NUCLEAR FISSION, which is the generation of energy from nuclei splitting via the bombardment of neutrons (nuclear reactors use this concept to split uranium and obtain energy).