GMAT Critical Reasoning (CR) | How to solve Argument Evaluation question?

Basically, I need to take both extremes that are given in the answer choices and see the answer strengthens and weakens the argument. Doubt - Should it weaken and strengthen the conclusion?
What if the answer choice only weakens or only strengthens? Can such a choice be eliminated?
Sometimes - see two potential answer choices strengthening and weakening - what do I do then?

Please help me clarify these doubts .

Thanks
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