This was an answer choice that I arrived at using process of elimination. Answer choice C didn't immediately strike me, but in fact, it is well supported upon further inspection.
Answer choice C states the associations of colours with spirits was an important precursor/foundation of later uses of wampum that did not rely on these associations.
Early in the passage, we are told that the wampum colours (white and purple) were associated with two different sprits (lines 18-25). Then we are told (lines 33-36) that these wampum were attached to string and were used for political messages. This is how answer choice C is supported.
Answer choice D on the other hand, it is never mentioned in the passage that belt wampum carried a different association of the same colour vs string wampum.
I hope this helps. Please let me know if you have any other questions!