An example of a simple argument that can cause trouble if taken too lightly, or if you rush through your analysis and response.
Conclusion: Gloves/mittens are NEVER needed to keep hands warm in winter.
Premises: One can keep one's hands warm by putting on extra layer of clothing.
(b/c keeping vital organs warm CAN keep hands warm)
As usual, correctly answering a "weaken" question depends on your ability to stay focused on the conclusion of the argument.
(A) This choice says that keeping hands warm is not important. If anything, this strengthens.
(B) Which layers keep vital organs warmER has nothing to do with the conclusion.
(C) This choice states that SOMETIMES (when temps are low enough for frostbite), it is not possible to keep hands warm by using the method described in the argument. This suggests that SOMETIMES it might be necessary to wear gloves, which clearly weakens the conclusion.
(D) This choice says there's an even better way to keep hands warm. If anything, this, again, strengthens.
(E) So? No effect on the conclusion whatsoever.
The correct answer is (C)