The Reason Sunspots Are Cooler Than the Photosphere Is That

The reason sunspots are cooler than the photosphere is that

A) they are points where streams of cool gas from the corona impinge on the photosphere, thereby cooling these regions.
B) their powerful magnetic fields inhibit the convective flow of the ionized gases of the photosphere.
C) they are holes in the photosphere that reveal the lower temperature gases in the deeper layers.
D) their powerful magnetic fields act on the atoms of the photosphere to prevent them from emitting light.