Let's take a look at the first paragraph, as it introduces the primary purpose of the passage as a whole. Basically, it says that before Brown v. Board, Thurgood Marshall presented other cases to the supreme court. The author claims that these cases laid the foundation for the success of Brown v. Board. The author spends the rest of the passage demonstrating how Marshall's strategy evolved, eventually leading to his successful effort to end school segregation.
In short, this is all leading up to how Marshall defeated the concept of "separate but equal."This is best reflected by answer choice C.
Although Marshall did eventually call attention to an unsound legal doctrine (separate but equal), he did not do so by focusing on the strategy of its successful challenger. I am not sure what this means exactly, and there is no support for it in the passage. This is why E is incorrect.
