The first sentence of the passage is the conclusion of the argument. The rest of the passage only provides an explanation. The second definitely looks like an evidence, not conclusion. However, it is not clear whether the first is an intermediate conclusion but it is certainly not a fact.

A. The first part provides evidence that, if correct, would weaken the main conclusion. Eliminate.
B. the second is a conclusion drawn in order to support the main conclusion. Eliminate.
C. the second is a claim advanced in support of the main conclusion of the argument. Eliminate.
D. The first is a finding whose accuracy is evaluated in the argument Eliminate.
E. The first part is a presumption that, if correct, would weaken the main conclusion; the second provides evidence in support of the main conclusion. Here, the role of the first part is cleverly but accurately given. Smokers would have quitted smoking with low tar cigs but opposite is likely.

Therefore, the correct option is E.