The composition of a star is abundant in hydrogen and helium, both of which are two of the lightest elements. Because they are very light, they are usually unstable. To becomes stable, hydrogen atoms spontaneously combine with each other through a radiation process called nuclear fusion, to yield helium atoms. This process requires very high energy in the form of heat. Therefore, these lighter elements are burned in order to keep the star alive with energy.
Therefore, the answer is D.
