Explanation
Correct answer: C.
Choice C is the best answer. "In addition" logically signals that Naff’s artifact collecting was separate from, and in addition to, her interviewing.
Why the other choices are wrong
Choice A
Choice A is incorrect because "in other words" illogically signals that the information about Naff’s artifact collecting restates the previous information about her interviewing. Instead, Naff collected artifacts in addition to conducting interviews.
Choice B
Choice B is incorrect because "on the contrary" illogically signals that Naff’s artifact collecting was contrary to her interviewing. Instead, Naff collected artifacts in addition to conducting interviews.
Choice D
Choice D is incorrect because "today" illogically signals that Naff’s artifact collecting is occurring in the present day. Instead, this activity occurred in the past, as indicated by the past tense verb "collected."