"All" was confusing

Hey @AlyonaHess, thanks for your post. The word "all" denotes a sufficient condition, not a necessary condition. Hope this helps. Please let us know if you have any additional questions.

Mehran, typo! In the answer B I was confused (and still is ) with ONLY, not "all". In B there is no "all";) Only indicates necessary, right? I diagrammed it: Not Progress - > Rp because it says " if there are only reasonable people". How can we ignore it and diagram: onlyRP - > Progress. Please help.

@mehran, I have the same question as @AlyonaHess - I diagrammed B out with "only" functioning as a necessary indicator, not as "onlyRP." Could you further clarify how "only" functions within this question? Thanks.

@AlyonaHess and @hales, Happy to help. Let's take a look. Here's our diagram of the stimulus: RP - >Adapt themselves to the world UP - >Try to adapt world to themselves Conclusion: Progress - >UP Based on that, we're trying to find the answer choice that must be true if all of those things are true. (B) says, "If there are only reasonable people, there cannot be progress." This is diagrammed as RP - >No Progress Progress - >/RP (UP) this is the same thing as what's being said in the conclusion of the stimulus (Progress - >UP) (B) is a contrapositive of the conclusion of the argument. If progress requires unreasonable people, then it must be true that if there are only reasonable people (meaning there aren't any unreasonable people), then there wouldn't be any progress. "If there are only" is telling us that there are no unreasonable people in the world and is basically the same thing as saying "if all people are reasonable," and this first part of the sentence is all in the sufficient condition. "Cannot" tells us that the part immediately after it is in the necessary condition and is negated. Thus, (B) is the contrapositive of the last statement in the stimulus and must be true if we assume everything in the stimulus to be true. Does this make sense? Let us know if you have any more questions!