Hi Cindy! You're right on the money for chaining those two conditionals together. Let me just go over that part quickly in case anyone else doesn't see how you got there. For Must be True questions like this, we want to look for a way to combine two parts of the stimulus together to make an inference. That's especially true when the stimulus uses conditional reasoning. Here, our stimulus gives us one conditional (the first sentence), a second conditional (the second sentence), and a third sentence that doesn't use conditional logic (it uses causal reasoning). With that setup, we can be pretty sure that the inference is going to come from combining those two conditional statements together, since the makers of the LSAT love to test your ability to combine conditional statements (they know it can be rather challenging!). Sure enough, for this stimulus we're able to chain those conditional statements together, just in the way you said:
First conditional: Squirrels survive
Intervention
Second conditional: Forest preserved
Squirrels survive
And so, like you did perfectly Cindy, those two conditionals in our stimulus can be combined to make the inference: Forest preserved
Intervention
Or, to put it in a normal English sentence: if large tracts of second-growth forest are preserved for squirrels, then it was with the intervention of conservationists. Like we do for every conditional, we also want to think about the contrapositive, which here would be: If conservationists do not intervene, then large tracts of second-growth forest will not be preserved for squirrels. That contrapositive matches answer choice (E) almost exactly, so (E) is our right answer.
Now, you got hung up on answer choice (B), and from previous responses in this thread it looks like you're not the first person to do so. But (B) is incorrect for two reasons.
First, (B) is wrong because it is not a conditional but an absolute declaration about what will happen. Let me give a simple example. Let's say we have a conditional that says "If I do the dishes, my apartment will smell better". An incorrect inference from that example would be "Some time in the future I will do the dishes and so my apartment will smell better", because we can't assume that there will ever come a time when I will actually do the dishes. In other words that inference is incorrect because it moves from a conditional ("If...then") to an absolute declaration ("This
will happen"). Similarly here, answer choice (B) is assuming that some conservationists will in fact intervene ("the conservationists who intervene to help"), when that's not an assumption we can make. (B) moves from a conditional to an absolute declaration.
But let's say we fix that problem by making answer choice (B) into a conditional. So now it would read something like, "If the conservationists intervene to help the squirrel monkeys survive, then some will do so by preserving second-growth forest habitat for the monkeys." However, it's still an incorrect answer choice! What's the problem now? Well, it's a Mistaken Reversal of our correct inference. Remember, our actual inference from the stimulus is Forest preserved
Intervention. But our new, conditional version of (B) is saying that Intervention
Forest preserve. Conditionals can only be read left to right; our correct inference leaves open the possibility that the conservationists intervened in some other way besides preserving the forest, so saying Intervention
Forest preserve is a Mistaken Reversal and therefore incorrect.
So to sum up, (B) is wrong for two reasons: 1) it's an absolute declaration rather than a conditional and 2) even if it were a conditional, it's a Mistaken Reversal. Hopefully that sheds a little more light on why (E) is right and (B) is wrong.
intervention 
C)
