The sun could have a small degree of influence on global warming, but it is not the main cause of the rapid rise in Earth's temperature. What evidence from the text supports this conclusion?
A: The sun's brightness varies slightly and regularly over time. The main cause of that dimmer-switch effect is sunspot activity. B: Since 1979, the sun's output has decreased while the Earth has warmed more rapidly than in any 30-year period for centuries. C: Clouds have a cooling effect on climate because they reflect the sun's energy. So fewer clouds could indeed lead to warming. D: Ionized molecules have electric charges. Ionized molecules might attact water molecules, causing clouds to form.