The Figure Shown Below Immediately Reveals That

The figure shown below immediately reveals that

A) disk material concentrates along the spiral arms but is completely absent between the arms.
B) spiral arms are sites where ongoing star formation happens efficiently.
C) disk galaxies do not contain any red, old stars.
D) the space between spiral arms must be filled with thick layers of invisible dark matter.
E) star formation happens only in the spiral arms of galaxies without bars.