Answer is D. "Global warming" is not a fact. It is a conclusion some draw from data or facts. The results section of a research paper documents the facts. The paper's discussion section includes conclusions the researchers have drawn.\
Global warming is more accurately a conclusive label of agreement for some people, but even then there are differences of interpretation on what, when, how, how much, etc. The same differences of opinion don't exist for a,b, and c.