Answer:
A. It will explain the distance scale.
D. It states what region or area the map covers
High mass stars are far more massive than the sun, and therefore have a much larger gravitational impact. A star of 100 solar masses (100x larger than the sun) has a much shorter life than that of the sun because the forces that cause the star to expand and "burn" have to work harder to overcome the much larger gradational impact. While the sun has a life span of approximately 8 billion years; the life of a red giant of 100 solar masses would be at best a few hundred million years because gravity will overcome the counteracting force of fusion. (resulting in a supernova, black hole, white dwarf, or other astronomical anomaly.)
