Explanation
Correct answer: C.
Choice C is the best answer. "In addition" logically signals that the claim in this sentence—that the Inca of South America may have used quipus to record more complex information—is an additional point related to the previous statement about the Inca using quipus to record countable information.
Why the other choices are wrong
Choice A
Choice A is incorrect because "as a result" illogically signals that the claim in the sentence is a consequence or result of the previous statement about the Inca using quipus to record countable information. Instead, the possibility that the Inca used quipus to record more complex information is an additional point about how the quipus were used.
Choice B
Choice B is incorrect because "in other words" illogically signals that the claim in the sentence is merely a paraphrase or restatement of the previous statement about the Inca using quipus to record countable information. Instead, the possibility that the Inca used quipus to record more complex information is an additional point about how the quipus were used.
Choice D
Choice D is incorrect because "for example" illogically signals that the claim in the sentence exemplifies the previous statement about the Inca using quipus to record countable information. Instead, the possibility that the Inca used quipus to record more complex information is an additional point about how the quipus were used.