I don't think they favour valid or invalid arguments in this question type. They just want you to parallel the reasoning structure. You're correct to suggest thats an invalid argument form. So the answer choice has to make that same error.
... , I'm working on analyzing arguments for strengthening, weakening, sufficient assumptions ... forms. Having gone through the valid and invalid argument forms lessons ...
... the difficulty or via the valid inferences we learned in CC ... with the 'some' & 'most' valid inferences.
Are you having ... chain? Sometimes I think the arguments and ACs are counterintuitive or ...
... trap that is attempting to memorize information in the passage as ... designed to test understanding of arguments and logic rather than fact ... nature of the LSAT (and arguments in general) means that the ...
Both arguments are making a correlation-causation ... argument was in reference to arguments like (1), which is why ... , so that observation/statement is valid.
Weakening/strengthening tend to deal with causal reasoning. Questions that deal with validity are going to be conditional reasoning oriented because causal arguments are never valid. As such, SA/PSAr/PSAa deal with conditional reasoning.