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I hope someone can explain this. I am not sure if I diagrammed it correctly, so please certainly do correct me.

A = "prehistoric humans were able to stand"
B = "making sophisticated tools"
C = "making advanced hunting weapons"
X = "free use of the hands"

We are asked to weaken this argument:

B requires X (B -> X), and A makes X possible (A -> X). Therefore, B required A (B -> A).

Now, this reasoning is already flawed as it takes for granted X -> A .

The correct answer says: C does not require A (how do you diagram this?). It seems that the logic is that if C does not require A, then X does not require A. This is an assumption on its own, and I can't find a support for it.

Perhaps I am looking at this in a wrong way, so I would appreciate any help.

The key here is realizing that "advanced hunting weapons" are a subset of "sophisticated tools". So, if (B) is true, then we have one type of sophisticated tool with a non-standing-upright human ancestor. The premise told us that creating such tools required the free use of the hands.

Therefore, if (B) if true, then it seems likely that those non-upright-standing human ancestors had, at some point, free use of their hands in order to make the tools (weapons). That makes it less likely that "free use of the hands" requires "standing upright."

Does that help?

It makes the whole difference!

At first I did pick the correct answer, but then noticed that "tools" were changed to "weapons", and I immediately concluded this was a trap. I would have never been able to see that "weapons" could be considered as a subset of "tools"... This question is really terrible. But I really do appreciate the help - thanks!