They are among the only types of organisms that get their energy from a non-living thing, and they give energy to Primary consumers, which give energy to secondary consumers, which give energy to tertiary consumers, which can give energy to decomposers, etc.
"A. Natural resources and human labour".
I agree.
The answer is option B "temperature." Greenhouse effect is the process of trapping the suns heat in the lower atmosphere. A increase of greenhouse effect would cause surface temperatures to rise. Which then contributes to global warming because of melting the ice bergs in cooler areas on Earth and causing waters to rise and creating storms. It's not option A because the sun gives off heat or harmful radiant waves which doesn't increase carbon dioxide levels. Wouldn't be option D because it would contribute but it wouldn't happen without a increase of temperature. It also wouldn't be option C because oxygen isn't relevant in this case.
Hope this helps.