In Figure 17-15, Both Regulus and Mira Are About 100

In Figure 17-15, both Regulus and Mira are about 100 times as luminous as the Sun. What is the primary source of their radiant energy?

A) These two, like all stars, derive their energy primarily from core nuclear fusion producing helium from hydrogen.
B) The core fusion of hydrogen to helium is insufficient to provide the energy for a star with 100 times the Sun's luminosity. Thus, both of these stars use more energetic reactions.
C) Regulus, like all main-sequence stars, relies on core fusion of hydrogen to helium. Mira, being a giant, relies primarily on more energetic reactions.
D) Mira has a surface temperature lower than that of the Sun, so core fusion of hydrogen to helium is sufficient to provide its energy. But Regulus is much hotter and must rely on more energetic reactions.