Hi Snowy!
You are very correct in nailing the correct question type, this is a MBT/Author's perspective. Keeping that in mind, it's important to realize the lens through which an author of an LSAT passage will view a celebrated legal hero, especially one from an underrepresented demographic.
That means that the general tone that the author will have toward Thurgood Marshall will certainly be positive, which helps to eliminate A and B here. I think E can fall short under a similar vein in that 'subjective' hardly seems unequivocally positive, and might even belie a slight dig. I think D loses in a large sense due to the importance of the concept of
necessary on the LSAT, especially in contrast with the idea of being
sufficient. In that sense, I feel 'sufficient' would have been better applied here in that his strategy did seem to be effective in reaching his legal goals. The term 'essential' is used in paragraph two, but it mentions specifically that a certain element was necessary for the test-case strategy, not that the entire strategy itself was
necessary for Marshall in his legal efforts.
A major theme in the LSAT reading comprehension is celebrating those individuals who are revolutionaries in their craft. Whether it be in art, science or law, individuals who push boundaries and exhibit progressive and innovative methods are given generally very positive treatment by the authors, and this passage follows suit.
The support for C comes subtly throughout the passage in the general praise for how Marshall took a creative path in his (line 10):"strategic and methodological legacy to the field of public interest law," but I see the most direct support for his strategy being
unprecedented from this phrase around line 13-15: "he and the NAACP developed innovations that forever changed the landscape of public interest law."
I hope that helps! Happy Friday