A main sequence star begins transforming into a red giant when
A)helium begins fusing.
B)helium within the core begins to expand.
C)contracting helium causes hydrogen to fuse.
D)hydrogen starts fusing within the core.

Question

Quizplus · Accepted Answer

A main sequence star becomes a red giant when the hydrogen in its core is depleted, causing the core to contract and heat up, which in turn causes hydrogen in the surrounding shell to start fusing.

A Main Sequence Star Begins Transforming into a Red Giant