I noticed there wasn't a post for this question and since I need practice with NA questions I thought I might one up. That being said, I would greatly appreciate it if others (especially instructors) chimed in to straighten out the hiccups in my reasoning!
From the question stem, I know this is a necessary assumption so I'm primarily on the lookout for either a "shielding" or "bridging" answer choice.
Premises
Two unrelated languages both have the same word ("dog") for canines.
+
Neither language could have borrowed it from either because both languages were already using the word long before they came into contact with each other
Conclusion
When languages share words, the similarity is due to neither language-relatedness nor borrowing.
The conclusion raised some flags for me because it assumes that just because the 2 languages only came into contact after the word was already in use by both that neither language could have borrowed it at all. This struck me as a huge gap because both languages could've been in contact with another country that also uses the same word. With that in mind, I realized that there was a good chance I would need an answer choice to "shield" this gap.
(A) Out of scope. This isn't something the argument needs in order for the conclusion to follow-through
(B) This one was very tempting. It was along the lines of the type of answer I was looking out for so I initially kept it. I eventually decided against it because I found a better answer but also because unlike the correct AC, this AC doesn't say that any of those languages came into contact, which I thought was key for closing the gap.
(C) Out of Scope. This doesn't do anything for the argument.
(D) This is exactly what I was looking for. This AC eliminates the possibility that both languages borrowed the word from a third party. Also, negating this AC would weaken the stimulus.
(E) I'm not sure how to classify this AC. It doesn't seem out of scope to me. It just seems like a premise booster; the stimulus already states that the 2 languages are unrelated and came into contact so this just seems like a reaffirmation of that.
Thank you for all the help!