#help#help It is a Must Be True Question, but according to JY's explanation, he said that if AC A is not met, then the conclusion must be invalid. So why can't we consider this question as a Necessary Assumption Question? I believe the Question Stem is looking for the necessary condition that would make the conclusion "substantially change" valid. I don't know why, but lately I often tend to approach other types of questions as if they were NA Questions. Does anyone else share the same confusion?

#help #helpThis might be a silly question. I approached this problem as an NA (necessary assumption) question and found that negate AC A would make the entire argument invalid. However, JY said it is a principle question, and I don't understand why. If it is an SA (sufficient assumption) question, that could convince me to some extent. Why am I confusing NA and SA? Does anyone else have the same confusion as me?