Why (A) is right: exposing an unrepresentative sample
A Weaken explanation from our free library. The question below is original, written for this page. Then the full breakdown: why the right answer is right, and why each wrong answer is wrong.
The question
A poll found that 80 percent of shoppers at an organic grocery store support a ban on plastic bags. Activists conclude that the ban enjoys broad public support.
Which one of the following, if true, most seriously weakens the activists' conclusion?
- The poll interviewed shoppers only at organic grocery stores in a single wealthy neighborhood. Correct
- Plastic bags are convenient for carrying groceries home.
- The poll asked about plastic bags rather than paper bags.
- Eighty percent is a large majority of the people who were polled.
- Several organic grocery stores have already stopped offering plastic bags.
Why (A) is correct
The conclusion is about the broad public. The evidence is about one narrow slice of it: organic-store shoppers in one wealthy area. People who shop at organic stores are exactly the people most likely to support a plastic-bag ban.
Choice (A) exposes the mismatch between the sample and the population the conclusion is about. A poll of the choir does not prove the whole town is singing.
Why the wrong answers are wrong
(B) Out of scope
Convenience is a reason to oppose the ban, but the conclusion is about what the public thinks, not about whether the ban is good policy. This does not touch the poll as evidence.
(C) True but irrelevant
The conclusion is about a plastic-bag ban, so asking about plastic bags is exactly right. This criticizes the poll for doing its job.
(D) True but irrelevant
This just restates the premise. Agreeing with the evidence is not a reason to doubt the conclusion drawn from it.
(E) Out of scope
What stores have done does not show what the broader public supports. The conclusion is about public opinion, and this is about store policy.
Last updated October 12, 2026