Logical reasoning PrepTest 139 · Section 4 · Question 9

Incorrect. The stimulus discusses the implications of each potential result of the analysis that the archaeologists are currently engaged in, but it's certainly possible that they'll fail to be able to make that determination. So this answer is unsupported.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Cultivated plants → Millennia earlier than known agriculture
(not Cultivated plants → Wild plants)
Wild plants → Occupants ate a wider variety of plants than contemporaneous people

Answer Anticipation:
The stimulus here brings up the implications of the two possible results of an analysis of plant life in a certain site. Both are presented as conditional statements, and we can even link the two types of plants based on the stimulus defining wild plants as uncultivated (not cultivated).

We can chain these together, but if we know the meaning of certain conditional structures, we can draw a conclusion without doing so.

That second conditional—the one based on defining wild plants as not cultivated—has a negated sufficient condition but a positive necessary condition. That structure—not A → B—means that at least one of the two terms is true. "If it's not one, then it's the other" is what it's saying. This is contrasted with the not both structure—A → not B—which says, "If it's one, then it's not the other."

So, based on that conditional, we can say the plants are either cultivated or wild. So, based on the conditionals, the people from this site either cultivated plants millennia before anyone else did, or they ate a wider variety of plants than anyone else did. Let's find an answer that reflects that.

Answer Explanation:
In defining "wild" as not cultivated, the argument establishes that plants are either cultivated or wild. The argument also establishes an implication of each of these possibilities. If they're cultivated, then the people at the site were engaged in agriculture millennia earlier than others—thus using plants in ways no one else was. If they're wild, then the people ate a wider variety of plants than anyone else at the time—thus using plants as food that other people weren't. Both cases see the people using plants in ways no one else did, thus supporting this answer.

Key Takeaway:
not A → B means at least one of A or B is true. Note the phrasing—at least one—leaves open the possibility that both are true, though that's not possible here as the two terms are mutually exclusive. That's because one is the negation of the other, though—it's not due to the conditional structure.

C → not D means not both of C and D can be true. Similarly, note that the phrasing here leaves open the possibility that neither can be true.

Incorrect. The stimulus notes that one possibility is that the people were eating more wild plants than others, but that's not the same as reaching a "more advanced stage" of using wild plants. And tying that to agriculture/cultivation is a jump.

Incorrect. This answer is a reversal of the first conditional statement.

Incorrect. The stimulus never discusses the relative likelihood of the two possibilities, so this comparison is unwarranted.