A common misconception on the LSAT is that “principle questions” are a thing. In fact, the word “principle” appears in multiple question types which you should treat very differently. The most important thing to look for when you see the word “principle” is whether the principle points up or down. Some questions (PSAa or Rule Application questions) give us a principle in the stimulus and ask us to apply it down to the answer choices. These are akin to Most Strongly Supported questions, where we must be cautious of overstrong language and stick only to inferences supported by the stimulus.

This question (a PSAr or Find The Rule question) does the opposite: it presents a bunch of principles in the answer choices and asks us to apply them up to the stimulus in an effort to justify the argument. These are akin to Strengthen questions, where overstrong language is completely fine and we’re hoping to bridge any gaps in the argument we can find.

PSAr questions tend to follow routine patterns, and our approach can therefore be similarly routine. First, it’s critical to identify the argument’s conclusion and the premise(s) that seek to support it. In a shockingly high proportion of PSAr questions, the correct answer will take the form: Premise → Conclusion.

Like in normal strengthen questions, though, it’s also important to note any common flaws you see, or (especially) subtle jumps from one concept to another (e.g. from talking about athletes to talking about professional athletes). Correct answers that address weaknesses like these are common as well.

This Environmentalist’s conclusion is marked quite clearly, and developing a precise understanding of the conclusion is always critical, so let’s start there. It’s a simple conditional statement that we’ll present using a few different wordings (all logically equivalent) for your convenience:

If you use GMO crops, you must test first.
Don’t use GMO crops unless they’ve been tested first.
If you haven’t tested, you can’t use GMO crops.

So okay: TEST THE DAMN GMO CROPS.

Now the support. Why is testing these crops so important?

Well in general, GMO crops are running rampant and risk wrecking a bunch of ecosystems. One example of this is some crop that we used a ton, realizing only later that it might hurt butterflies.

This stimulus calls for the familiar Premise → Conclusion anticipation: we want some version of “Don’t do stuff that risks destroying ecosystems unless you’ve tested it first.”

It would be okay for the principle to go overboard in supporting the conclusion – “Never do anything unless you’ve tested it first” would also work – but going overboard by supporting a claim beyond the conclusion is often a red flag: “We should ban GMOs altogether” might be an overboard expression of the Environmentalist’s worldview, but it doesn’t give us a reason to test GMOs, which is what the argument needs.