This is how I got it right -
Structure of the argument:Conclusion: the significance of Charles Walcott's finding is in its reflection of recent classification, not in his own findings.
Premise: Charles Walcott is prominent.
Restated conclusion (indicated by "thus"): Charles Walcott only confirmed what was already given.
Answers:(A) It draws conclusions about the merit of a position and about the content of that position from evidence about the position's source.
// Source of the evidence is Charles Walcott. Correct.
(B) It cites two pieces of evidence, each of which is both questionable and unverifiable, and uses this evidence to support its conclusions.
// There is only one piece of evidence. Incorrect.
(C) It bases a conclusion on two premises that contradict each other and minimizes this contradiction by the vagueness of the terms employed.
// There is only one premise; both conclusions support each other. Incorrect.(D) It attempts to establish the validity of a claim, which is otherwise unsupported, by denying the truth of the opposite of that claim.
// The argument did not deny the opposite of the claim (e.g. denying that Charles Walcott did not confirm the classifications). Incorrect.
(E) It analyzes the past on the basis of social and political categories that properly apply only to the present and uses the results of this analysis to support its conclusion.
// There is no discussion about past/present/social/political aspects. Out of scope. Incorrect.