Critical Reasoning

Being articulate has been equated with having a large vocabulary. Actually, however, people with large vocabularies have no incentive for, and tend not to engage in, the kind of creative linguistic self-expression that is required when no available words seem adequate. Thus a large vocabulary is a hindrance to using language in a truly articulate way.
Which one of the following is an assumption made in the argument?
(A) When people are truly articulate, they have the capacity to express themselves in situations in which their vocabularies seem inadequate.
(B) People who are able to express themselves creatively in new situations have little incentive to acquire large vocabularies.
(C) The most articulate people are people who have large vocabularies but also are able to express themselves creatively when the situation demands it.
(D) In educating people' to be more articulate, it would be futile to try to increase the size of their vocabularies.
(E) In unfamiliar situations, even pe0ple with large Vocabularies often do not have specifically suitable words available.

OA is A

IMO A?

IMO A
B is incorrect because we talk about people who have large vocabulary.
But B is other way round.

Conclusion: Large Vocab = Hindrance to being articulate

Evidence: People w/vocab have no incentive & don't engage when no avail words are adequate

Assumptions: "Truly articulate" = "creative self-expression"; the vocab they already have/use is not enough to be considered "truly" articulate

Notice how our prediction of the assumptions almost exactly matches A. The idea here is to LINK the fact that the author is defining what it means to be articulate and stating that a certain type of people do not fit that definition.

E does not specifically relate to the fact that a "creative self-expression" in the presence of a lack of "available words" is required to be articulate. Also, the idea of an "unfamiliar situation" is outside the scope of the argument.

P1: Being Articulate is related to vocabulary.
P2: But people with large vocab do not take part in create self expression required when no available words seem adequate
C: Therefore large vocab is hindrance to use language in articulate way

Author supports his conclusion on the premise that people do not use self-expression required when no available words seem adequate. That means he assumes that articulate people should use self-expression required when no available words seem adequate and this is stated in A.

B: Irrelevant, we are discussing about people who are not able to express.
C: General Options can never be assumptions.
D: Too strong
E: Unfamiliar situation is not described, Also if it is true but not an assumption.

I see the logic here hard. Is this LSAT question? some LSAT questions are not similar to gmat ones.

what is the source?