Why Is the Temperature at the Region of a Sunspot

Why is the temperature at the region of a sunspot cooler than the photosphere

A) They are holes in the photosphere that reveal the lower temperature gases in the deeper layers.
B) They represent points where streams of cool gas from the corona lower the temperature in those regions of the photosphere.
C) Powerful magnetic fields in the sunspots act upon the atoms of the photosphere to prevent them from emitting light.
D) Powerful magnetic fields inhibit the convective flow of the gases of the photosphere downward, allowing them to cool for longer than would normally be permitted.