In massive stars, three helium nuclei fuse together, forming a carbon nucleus, and this reaction heats the core of the star. The net mass of the three helium nuclei must therefore be
A. the same as that of the carbon nucleus because mass is always conserved.
B. the same as that of the carbon nucleus because energy is always conserved.​
C.less than that of the carbon nucleus.​
D.higher than that of the carbon nucleus.​