The Centers of the Granular Cells on the Surface of the Sun

The centers of the granular cells on the surface of the Sun appear to be brighter than the edges of the cells because

A) higher magnetic field strength at the centers condenses and heats the gases there.
B) the centers are composed of gases that are different from the gases that compose the edges.
C) gases at the centers are more transparent than gases at the edges, allowing astronomers to view deeper and hotter layers.
D) the centers are hotter than the edges.