In the Post-Main-Sequence Stages, High-Mass Stars Follow Quasi-Horizontal Paths in the H-R

In the post-main-sequence stages, high-mass stars follow quasi-horizontal paths in the H-R diagram.This means that

A) their luminosity increases because they expand.
B) their color gets redder because they expand.
C) their surface temperature stays about the same because their luminosity stays about the same.
D) they become supernovae immediately after leaving the main sequence.
E) they collapse and become very small in size.