The question asks, "The focus of which one of the following books would most clearly reflect the current interest of the folklorists mentioned in the last paragraph?"
(C) says, "a study of the purpose and meaning of a tale or song for the men and women in a particular culture"
We're looking for an example of a book that'd reflect the contemporary interest of the folklorists from the last paragraph of the passage. In lines 49-52, we're told about "the current interest of folklorists in viewing folklore in context and thus answering questions about what folklore means to the people who use it." This is is what we're looking for in an example, and (C) provides us with exactly this. A study of the purpose and meaning for the men and women in a culture is an excellent example of "what the folklore means to the people who use it" (lines 51-52).
(B) says, "a compilation of tales and songs from both men and women covering a great variety of traditional and nontraditional topics"
The problem with (B) is that this answer choice only describes the stories, but it doesn't describe context around and behind said stories. We're looking for information behind the stories, and this answer doesn't give us that, so we can get rid of it.
Does this make sense? Let us know if you have any more questions!