How will the right answer fit in terms of support and conclusion?

Only the right answer will add support that guarantees the conclusion.

Highlight the main conclusion in the passage, if there is one:

gesturing helps speakers quickly find the phrases they want.

[BACKGROUND]. [BACKGROUND]. [SUPPORT]. This indicates that [CONCLUSION].

It’s not the most obvious, but the conclusion changes the subject a little. Just because you “spoke more quickly” doesn’t mean you “quickly find the phrases” you want. I could find my phrases instantaneously but just keep quiet anyway. The right answer will connect these slightly different phrases together.

Map the wording of the answers to the wording of the passage:

(A) …regularly gestures when speaking quickly…

Cool story. This doesn’t connect to the “find the phrases” part of the conclusion at all though, so this doesn’t add support.

(B) The cartoons were chosen…

Nobody picked this one, right? How the cartoons were chosen has nothing to do with the conclusion’s claim about “gesturing”.

(C) …quicker speech and less repetition helps speakers find the phrases they want quickly.

I couldn’t have said it better myself. Here’s a direct connection between the wording in the support and the wording in the conclusion.

(D) Any form of behavior that helps speakers quickly find the phrases…

Tricky, since it feels like all the wording in this maps to wording in the passage. But it’s explaining something else you would know about a behavior that you already know helps people “find the phrases they want”. That’s going way beyond the conclusion, which is just trying to establish that “gesturing helps” with finding phrases in the first place. What happens after we know that is outside the scope.

(E) …the most quickly and repeated themselves least…

This is bringing in extreme terms that don’t map to the comparison made in the passage. The support only says “more quickly and repeated themselves less.” We can’t assume anything about the quick-est talkers.

(C) is the correct answer.

Common pattern/s in this question: It may not have seemed like a big deal, but you’re a lawyer now. You gotta recognize that when the conclusion brings in a new idea like “find the phrases”, the argument has changed the subject. Right answers will pretty much always make the connection.