Critical Reasoning (CR) | Re: Professor: The author's reconstruction of the street system of

B. The first is meant as a concession to a position that the argument rejects; the second is meant to undermine a potential objection to a premise of theargument.

The first part of this choice is correct. After all, in saying that an assumption that supports "the author's reconstruction" is "not an reasonable assumption," the first boldfaced portion concedes that at least part of "the author's" reasoning, which the argument rejects, is reasonable.

The second part of this choice is correct as well since the second boldfaced portion indicates that the objection "later structures replaced earlier ones on the same alignment" is not supported by evidence. In other words, the second boldfaced portion serves to "undermine" thatobjection.

Keep.