Hi Naminyar,
It's
not a Strengthen stem, but this is a good example of how LSAC plays with your preconceived notions. So let's break it down:
Here's the full stem: "The principle stated above most helps to justify the reasoning in which one of the following arguments?"
From the start, we can tell it's a principle question: ""The principle stated above..." So, whatever the main stem turns out to be, this will have a PR overlay on it. Easy so far
Next, they throw in something that should be familiar to everyone: "...most helps to justify the reasoning..." That would normally be a Strengthen stem (due to the "most"), and so many readers simply say, "Oh, it's a Strengthen-PR question. Got it!"
BUT, look how they framed that idea (italics added): "The principle
stated above most helps to justify the reasoning
in which one of the following arguments?" This means that an idea in the stimulus is being used to determine the answer, which is a classic First Family information arrangement (arrow pointing down from the stimulus to the answers). Strengthen questions are Second Family (arrow point up), so we know right now this isn't a Strengthen question.
In the First Family, what would be similar to "most helps to justify" an answer choice? Since its telling you to use the principle in the argument to "prove" an answer, that would be closest to Most Strongly Supported, and that's what this is ultimately. We'd put it down under Must-PR since Must includes MSS for us.
Overall, an excellent exercise in showing that you simply can't assume that the appearance of certain code words ("most helps to justify the reasoning" in this case, or "strengthen" in another popular example) automatically means you can classify the stem. Instead, you have to see what they do with that language.
Please let me know if that helps, thanks!