What Is the Best Reason Astronomers Have Come Up with to Explain

What is the best reason astronomers have come up with to explain why sunspots are cooler and look darker?

A) Sunspots are holes (less dense regions) in the Sun's photosphere, through which we can see the darker regions of the Sun below
B) Sunspots are places where the strong magnetic fields in the Sun resist the upward motion of bubbling hot gases from underneath
C) Sunspots are regions where carbon clouds high above the photosphere gather and these dark clouds block the light from underneath them
D) Sunspots are regions in the upper chromosphere where there is a lot of coronium, which absorbs light
E) Sunspots are so mysterious and difficult to explain, astronomers really don't have idea what causes them
Section 14.3: Solar Activity above the Photosphere