Fusion reactions constitute the fundamental energy source of stars, including the sun. hydrogen “burning” initiates the fusion energy source of stars and leads to the formation of helium. generation of fusion energy for practical use also relies on fusion reactions between the lightest elements that burn to form helium. in fact, the heavy isotopes of hydrogen—deuterium and tritium—react more efficiently with each other, and, when they do undergo fusion, they yield more energy per reaction than do two hydrogen nuclei. the hydrogen nucleus consists of a single proton. the deuterium nucleus has one proton and one neutron, while tritium has one proton and two neutrons. what conclusion can be drawn from this information? a) deuterium and tritium are required to burn hydrogen. b) the most efficient fusion reactors would use two hydrogen nuclei. c) the most efficient fusion reactors would use heavier forms of hydrogen. d) helium occurs naturally. the burning of hydrogen is not required to get helium in nature.