Answer (D)

@Julie-V, Happy to help. Let's look at (A) and (D). This question is a strengthen with a necessary premise question, so if the negation of an answer choice wrecks the argument, then we know that it's the correct answer choice. (D) says, "In educating people to be more articulate, it would be futile to try to increase the size of their vocabularies." (D)'s negation is, "In educating people to be more articulate, it would not be futile to try to increase the size of their vocabularies." The world "futile" in (D) is too strong. It's totally possible that increasing the size of someone's vocabulary could be helpful to a point in improving their articulation, but that having a really large vocabulary is still a hindrance to being articulate. If someone's vocabulary is one word and it goes up to 100 words, it could help them be more articulate, and their vocabulary still wouldn't be super large. (D)'s negation doesn't wreck the argument, so we can get rid of this answer choice. (A) says, "When people are truly articulate, they have the capacity to express themselves in situations in which their vocabularies seem inadequate." (A)'s negation is, "Being articulate does not require having the capacity to express oneself in situations where one's vocabulary seems inadequate." The stimulus states that people with big vocabularies tend not to use this capacity, so it is assuming that that being articulate does require this capacity. (A)'s negation makes the argument fall apart, so it's the correct answer choice. Does this make sense? Let us know if you have any more questions!

I'm having a lot of trouble with the negation of question A. Are you getting to that wording by showing sufficient where there is no necessary premise?

Sorry - answer choice A*

Hi @shafieiava, Negating a conditional can be pretty tricky, but in general, the negation of a conditional A - >B can be expressed as A & ~B, which is kind of what you're getting at - the sufficient premise is there, but the necessary one isn't. For example, if we're told that "all men are mortal," or Man - > Mortal, how do we negate this? We show that some men are not mortal, or that there exists at least one man who isn't mortal, which is Man & Not mortal. Hope this helps!