This one is tricky because of the "Thus" which usually indicates conclusion. The first sentence, however, is supported by that (subsidiary) conclusion.
Conclusions can do 3 things. Disagree, interpret evidence, or make a recommendation. Sentences that don't do one of these things can't be our conclusion. Sentence 2 just states an idea with no justification, so it's out. Sentence 3 (the "Thus") kinda sorta (poorly) follows from sentence 2, but it's a bit of a stretch. If we accept that as true, however, it provides evidence for Sentence 1, the actual conclusion.