CR: Weaken questions

[cesar.rodriguez.blanco]

What are the most common types of correct answers in "weaken a Conclusion" question?
For example, in Strengthen the conclusion, the premise should do at least one of the following:
1) Fix a weakness of the conclusion OR
2) Validate an assumption made by the argument OR
3) Introduce additional supporting evidence.

but for WEAKEN, what is the approach?

[esledge]

A conclusion may be weakened by:
(1) striking down an assumption
(2) partially countering an assumption
(3) offering a countering premise

Note: These will often require the choice to introduce "new" information not mentioned in the original argument. Such new information is NOT automatically "out of scope" and therefore wrong.