Alana drew a diagram to compare the life cycles of low-mass and high-mass stars. which labels belong in the areas marked x, y, and z? a.) x: nuclear fusion forms hydrogen in the main sequence star. y: a white dwarf is part of the cycle. z: a supernova is part of the cycle. b.) x: a white dwarf is part of the cycle. y: nuclear fusion forms hydrogen in the main sequence star. z: a supernova is part of the cycle. c.) x: a protostar is part of the cycle. y: it begins in a nebula. z: nuclear fusion forms hydrogen in the main sequence star. d.) x: it begins in a nebula. y: nuclear fusion forms hydrogen in the main sequence star. z: a protostar is part of the cycle.