In the Greenhouse Effect, What Is the Direct Cause of Extra

In the greenhouse effect, what is the direct cause of extra heating of the Earth's surface?

A) Additional carbon dioxide makes the atmosphere more opaque to infrared light, trapping part of the blackbody radiation that would normally escape into space.
B) Additional carbon dioxide makes the atmosphere more transparent to infrared light, allowing the sun to more directly heat the surface.
C) Additional carbon dioxide makes the atmosphere denser, and thus heat passes through it more slowly.