Professor: The author's reconstruction of the street system of

Professor: The author's reconstruction of the street system of medieval Constantinople is based on the assumption that the position of present-day structures constitutes evidence of medieval street alignment. While this is not an unreasonable assumption, the author's reconstruction is suspect because, for one thing, the structures that are alleged to preserve medieval street alignments are of widely differing dates spanning fourteen centuries. Some may claim that later structures replaced earlier ones on the same alignment, but there is no archaeological evidence to support this.

The passage is about "the author's reconstruction of the street system of medieval Constantinople."

The passage begins by presenting an assumption upon with "the author's reconstruction" is based:

The author's reconstruction of the street system of medieval Constantinople is based on the assumption that the position of present-day structures constitutes evidence of medieval street alignment.

The passage then offers a concession regarding that assumption:

this is not an unreasonable assumption

By saying the above, the argument concedes that, at least, an assumption underlying "the author's reconstruction" is reasonable.

Then comes the main conclusion of the passage:

the author's reconstruction is suspect

Then, the support marker "because" introduces evidence in support of the main conclusion:

for one thing, the structures that are alleged to preserve medieval street alignments are of widely differing dates spanning fourteen centuries

A potential objection to that support is mentioned:

Some may claim that later structures replaced earlier ones on the same alignment

Finally, that potential objection is countered:

there is no archaeological evidence to support this

Which of the following most accurately describes the roles played in the professor's argument by the two portions in boldface?

A. The first is a premise meant to support the argument's main conclusion; the second is presented as a rebuttal of a cited objection.

The second part of this choice is correct. After all, the purpose of the second boldfaced portion is to counter an objection to the support for the main conclusion.

However, the first part of this choice is incorrect since the first is not a premise. Rather, it's a concession that an assumption supporting a position that that argument opposes is "not ... unreasonable." So, the first does basically the opposite of supporting the argument's main conclusion since it concedes that part of an argument that the conclusion opposes is reasonable.

Eliminate.

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 the argument.

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" that objection.

Keep.

C. The first states a criticism of the position that the argument opposes; the second is a premise meant to directly support the argument's main conclusion.

The first does not state a criticism of the position that the argument opposes. Rather, the first does basically the opposite of stating a criticism by conceding that at least an assumption on which the position is based is reasonable.

Also, the second does not "directly support" the main conclusion. Rather, it indirectly supports the main conclusion by countering an objection to the support for the main conclusion.

Eliminate.

D. The first expresses partial agreement with the position that the argument rejects; the second is the position the argument rejects.

The first does not "express partial agreement with the position that the argument rejects." Rather, the first concedes that an assumption on which that position is based is reasonable. Conceding that an assumption is reasonable is not the same as partially agreeing with the position itself.

The second is not the position the argument rejects. Rather, the second states a reason to reject that position.

Eliminate.

E. The first anticipates and rejects a criticism to which the argument could be susceptible; the second denies an assumption upon which an opposing argument rests.­

The second part of this choice is close to correct since the second boldfaced portion could be seen as denying that "later structures replaced earlier ones on the same alignment," which could be seen as an assumption on which the position the argument opposes rests.

At the same time, we can confidently eliminate this choice since the first boldfaced portion does not "reject" anything. Rather, the first concedes that an assumption is "not ... unreasonable," in other words, that the assumption is reasonable. Conceding that something is reasonable is basically the opposite of rejecting it.

Eliminate.

Correct answer: B