Correct Answer: B
Explanation:
Since Dave's comments don't challenge what Sue says, we can eliminate answers E and C (mitigate = lessen). His comments reinforce what she says and so A sounds tempting but is wrong since Dave talks about pollution in general and doesn't mention carbon dioxide. Of the remaining choices, B is best since Dave does give information that suggests, like Sue, that we should take fewer flights. (D is incorrect mainly because Dave is not talking about the "effect" of pollution. Note how careful you have to be that all the words in an answer are exactly right.