GRE Verbal Reasoning Practice Questions Book RC Practice Set Medium

This question is with reference to Official GRE Verbal Reasoning Practice Questions Book RC Practice Set Medium Page 26 - Passage “Frederock Douglas was unquestionably the most famous African American…”

Q9 asks about evidence used by Douglas against racial inequality - I understand the passage mentions “but he offered his entire career and all his achievements as living proof that racists were wrong in their belief that one race could be inherently superior to another”.
But he also mentions that “His favorite rhetorical strategy was to expose the hypocrisy of those who, while professing adherence to the ideals of democracy and equality of opportunity, condoned slavery and racial discrimination.”

By that reasoning why isnt C a better answer?

Note that the sentence right after the doctrine is mentioned says what Douglass did to fight it - i.e., used his life story.

Choice C isn’t obviously connected to the doctrine and it’s in a different paragraph, in which the passage isn’t discussing the doctrine anymore.

This is a skill I teach a lot: location. Using keywords (in this case, the doctrine) to guide you where to pay attention.