The passage never suggests that the SNCC is superior (preeminent) to other civil rights organizations. Even if (A) were supported, it would not be the purpose of discussing the SNCC. The purpose is to describe one of the consequences of the original sit-ins.

The discussion of the SNCC is a description of one of the consequences of sit-ins. Although the activities of the SNCC were different from sit-ins, the author’s purpose was not to tell us about those differences.

The purpose of discussing the SNCC is to present one of the consequences of the original sit-ins. Freedom Rides were the other consequence. Although the author does state that the Freedom Rides were a more clear “turning point” in the civil rights movement, that doesn’t mean the SNCC was discussed merely as background context.

(D) fits what we can predict before going to the answers. The purpose is to present one of the consequences (“important outgrowth”) of the original sit-ins.

The discussion of the SNCC is not connected to any requirements for local sit-ins. Although the SNCC may have been an organization that worked across the U.S., that doesn’t mean local sit-ins required an organization with such national reach. Even if (E) were supported, it still would not be the purpose of discussing the SNCC. The purpose was to describe one of the consequences of the original sit-ins.