I would think the answer is A, though this is a hard question to answer. But using deductive reasoning, we can answer it pretty well. The reason B and D wouldn't work is because we both know that the Greenhouse Gases and the Greenhouse Effect itself is making the Earth go through it's warm cycle just a tad faster than it should, so to say that the gases are causing the earth to become colder doesn't make sense, so B and D are no longer options, which leaves you with A and C. Although it makes sense to say that the gases would radiate the heat, it doesn't make sense to say that the heat is being radiated out of the atmosphere and into outerspace, because the actual issue is the fact that the gases are trapping the heat, so therefore C doesn't make much sense either, which leaves us with A. To explain why A works, you can say exactly what A says: The gases are absorbing and trapping the heat, which is causing the earth and climates in the earth to become warmer.
I hope I helped! And if you see a problem with my answer or need more information from it, please tell me! :D
