Why Do Sunspots Appear Dark in Pictures of the Sun

Why do sunspots appear dark in pictures of the Sun?

A) They are too cold to emit any visible light.
B) They are holes in the solar surface through which we can see through to deeper,darker layers of the Sun.
C) They are extremely hot and emit all their radiation as X-rays rather than visible light.
D) They actually are fairly bright,but appear dark against the even brighter background of the surrounding photosphere.