I am an LSAT tutor that has been working for 4+ years and love to provide in depth analysis to help improve the way my students are approaching the LSAT and in particular the difficult questions. Recently, multiple students have come to me with questions about this problem from Prep Test 85. Other online explanations of this problem (even those provided by some of the big prep companies) are not super helpful. I’m posting this to clear up questions you may have about this problem & as an example of the type of personalized tutoring I provide.

Post in the comments with any additional questions about this LR problem! I also have availability so if you like what you find below please feel free to reach out to me on reddit or email me at: lsattutor1995@gmail.com

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It seems to me like you did a great job eliminating answers A, B, & E and then struggled to determine whether C or D was the best answer. That's a great start & it's unsurprising to me that you're scoring in the low 170's. But, to hit your target of 175, it'll be important to start consistently choosing the correct answer once you've narrowed it down to 2. Let's talk about how to do that here.

For both C & D, you listed a few things that you didn't like about the answer choice. This is a great strategy when you're doing your first pass through the choices—If you hit upon an answer that you have no criticisms of, then we're golden. But here, you found that there was no perfect answer. What I'd like to see you doing at that point is going back to your candidate answers (C & D) and thinking about what is good about them.

In particular, it would be good to look at the answer choices and ask this question: "to what extent does this answer choice resemble an assumption that is necessary to this argument & about which I would have no problems?" Stop reading at the bottom of this paragraph & take a second look at answer choices C & D. What would you modify to make you satisfied with them as necessary assumptions?

OK. Maybe one of the answer choices is standing out to you now. Or, maybe neither of them resembles a necessary assumption to you. Let's talk about the types of assumptions we want to be alert to. Your notes on D make it seem like you were attuned to conditional relationships in the stimulus. It is possible to construct some conditional statements from the argument given but (as I think you found) it's somewhat awkward. It's not true, for example that SURVIVE → (EAT MANY TYPES OF FOOD). What seems to be true instead is that eating many different types of food makes fish more likely to survive. I think it would be good for you to review the types of inferences that can be made from categorical and comparative statements.

Consider this: In order for it to be the case that Atlantans are more likely to have cars than New Yorkers, it has to be true that at least one New Yorker does not have a car. Applied to this situation, since "Fish raised in experimental hatcheries [...] are more likely to survive after their release," it must be the case that some fish raised in traditional hatcheries do not survive after release. This is a necessary assumption because if every fish raised in a traditional hatchery survived, it would be impossible for a higher proportion of experimental hatchery fish to survive.

Adding in the argument's claim that experimental fish are more likely to survive because they are bolder, we arrive at this inference: some number of fish raised in traditional hatcheries die after release because they are not bold enough. If no traditional fish died because of timidity, there would be no room for boldness to improve the survival rates of experimental fish.

This inference resembles but is not identical to the assumption in C. "Some fish raised in traditional hatcheries die because they are too timid in their foraging for food." D does not resemble any valid inference to the same extent, so I think C is the better answer.