Logical reasoning PrepTest 133 · Section 2 · Question 14

Incorrect. This answer is a reversal of what the stimulus says—there, a necessary condition for considering a substance addictive is established ("only if"), not a sufficient condition. If this answer were true, water would be an addictive substance!

Incorrect. The stimulus doesn't establish what the definition that currently holds sway is, just what medical experts believe and what "some" suggest.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:
Addictive → Withdrawal from habitual use causes most users extreme difficulty

Answer Anticipation:
Yep, that's our Summary. Why is it so short? Well, the rest of the statements are things that are set up as not true—the view that "[s]ome have suggested" contradicts the view of medical experts, whose view is taken as determining what "[a]ny adequate" definition of addictiveness must include.

So this entire stimulus boils down to a single conditional relationship—addictive substances must cause withdrawal in most habitual users. While the answer might bring in other details, this strong statement (or its contrapositive) will almost certainly serve as the core of the correct answer as the only statement established as true that's also strong enough to support an inference:
Addictive → Withdrawal causes most habitual users pain
Withdrawal doesn't cause most habitual users pain → not Addictive

Answer Explanation:
First, let's translate "is not true for most habitual users" as it's going to be important to see if this lines up with the conditional, since it includes all the terms from the key conditional we identified. What is it saying can't be true for most habitual users? That some habitual users can stop using them without difficulty. So that necessary condition ("only if") can be rephrased as "most habitual users can't stop without difficulty." So the conditional is: Addictive → Withdrawal causes most habitual users pain, which matches what the premises says, so this is the correct answer.

Key Takeaway:
We went a little further than we would on the test to prove a point in this Summary, but Must Be True questions that feature opposing points that are shown to be wrong and weak statements tend to have answers that are based on a single or subset of statements in the stimulus. If one statement sticks out as stronger than the rest in a Must Be True stimulus, it's almost certain that that statement will play a role in supporting the correct answer.

Incorrect. The stimulus discusses withdrawal from the substance causing difficulty as a criteria for determining a substance is addictive, not psychological/physiological difficulty in using that substance.

Incorrect. First, the stimulus is about defining "addictiveness," not addiction. One is about a substance, the other is about a behavior. Second, the Expert at least starts to define addictiveness, so it's unsupported to say that defining it is "impossible."