Question

Why does a star grow larger after it exhausts its core hydrogen?
A) The outer layers of the star are no longer gravitationally attracted to the core.
B) Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper
layers outward.
C) Helium fusion in the core generates enough thermal pressure to push the upper layers outward.
D) Helium fusion in a shell outside the core generates enough thermal pressure to push the upper layers
outward.
E) The internal radiation generated by the hydrogen fusion in the core has heated the outer layers enough
that they can expand after the star is no longer fusing hydrogen