Read these lines: "I have no data yet. It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts." What job does the last of the quoted sentences do?

1. The middle sentence gives a warning: do not build a theory before the facts are in. 2. The last sentence then describes what goes wrong when the warning is ignored, since facts get bent to fit the theory. 3. Describing the harm is what makes the warning worth heeding, so the sentence supplies the reason. 4. It adds nothing new and takes nothing back, which rules out the second and third choices. 5. So it gives the reason why the warning matters, option D. _Source: Arthur Conan Doyle, The Adventures of Sherlock Holmes (1892), A Scandal in Bohemia_