Why Does a Star Grow Larger After It Exhausts Its

Multiple Choice

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) Helium fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward.
C) Hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward.
D) 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.
E) Helium fusion in the core generates enough thermal pressure to push the upper layers outward.