Hi, in this question we are looking to fix the argument- to find an answer choice that, if true, would make the argument valid.
Here the argument is flawed because the author wrongly assumes that a language's lack or presence of a term indicates its speakers lack or presence of that concept. This doesn't have to be true: perhaps I recognize that my mom's brother is different from my dads brother even if I don't have an exact term to describe that (such as maternal or paternal uncle. The author wrongly assumes that this is not possible, so to make the argument correct we must show that this is not possible.
B does this. If every language has a word for each quality it's speakers can distinguish, that we have that 1-1 relationship between words and understandable qualities.
D does not. D suggests that common words express common categories that people understand but it does not eliminate the possibility that someone can understand that category without a word for it.
