The question says, "Based on the passage, Ellison’s critics would most likely have responded favorably to Invisible Man if it had..."
(C) says, "contained a tribute to the political contributions of African American predecessors"
In the passage, the critics never complained that Ellison didn't write tributes to the political contributions of African American predecessors (people like W.E.B. DuBois) at the beginning of the novel "Invisible Man." Therefore, we don't have a good reason to think that this would have made the critics respond more favorably, so we can get rid of (C).
(A) says, "created a positive effect on the social conditions of the time"
In looking at the critics' complaints about the novel (in lines 9-16), we see that "his allegiance to the concerns of the individual prevented him from directing his art more toward the political action that critics believed was demanded by his era's social and political state of affairs, and that his indulging in European fictional modes lessened his contribution to the development of a distinctly African American novelistic style."
From this, we know that if Ellison had attempted to spark political action in his novel or if he worked more to help contribute to the creation of a distinctly African American literary form, it is likely that the critics would have had more favorable opinions of his novel. In looking at (A), it's basically saying the critics would have responded favorably if "Invisible Man" had had a positive effect on the social conditions of the time. Based on lines 9-16, we have strong support for this, as the critics probably would not complain that Ellison did not attempt to ignite political action, making them probably have more favorable reviews of the novel. Thus, (A) is the correct answer.
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