I don't think anything about this passage was easy.
This is one of my least favorite RC passages+questions.
I think the choice between (C) and (D) is one of those battles we commonly face in Main Point questions, which is "These both seem accurate, so which one is a better encapsulation of the Main Point?"
Sometimes, after we take a 1st pass through the answers, we're left with a couple choices that seem legit.
At this point, I start asking myself, "Which answer choice wraps its arms around more of the passage?"
This is important because many wrong answers on Main Point are true, but too narrow. That's the biggest problem with (D).
(D) only discusses the cakewalk at the beginning of the 20th century vs. Walker's cakewalk. So (D) doesn't touch on the 1st or 2nd paragraph at all ... those paragraphs give us the background of the dance in West-African traditions and bring us up to the end of the 19th century.
(C), meanwhile, references the dance's
original blend of satire and cultural preservation (2nd paragraph). It also says that Walker popularized the cakewalk (1st paragraph's big claim).
(D) does not say that Walker popularized the cakewalk. It refers to a version popularized by her, but that's a more limited claim.
Saying she popularized a version of the cakewalk isn't as impressive as saying she popularized the cakewalk, which is the main claim from the 1st paragraph.
===
Another filter I apply to Main Point questions is "which remaining choice sounds the most like the Most Valuable Sentence(s)?"
I tend to read RC passages for a Most Valuable Sentence (or two). So if I have identified a sentence or two as the "big ideas", then I also compare my remaining answers to that sentence.
For this passage, I would have said that the first sentence and lines 45-49 were the two big ideas.
-- Walker is noteworthy because she popularized the cakewalk
-- She did so by interpreting it in ways that would appeal to her differing audiences
(C) effectively combines those two thoughts.
==
Another filter I often apply to RC answers choices is "Are there are any extreme words that make me nervous?"
(D) contains the extreme word
primarily. Can we justify that in the passage? The passage certainly discusses the layers of parody that went into the cakewalk, but just because that's primarily what the passage discusses, we can't necessarily say the dance was primarily parodic in nature.
This last complaint is a little nit-picky, but with all 3 filters, I see (C) winning, so I get a much more cumulative sense of confidence in picking it.
Hope this helps.