S & N Statement for If and Only If

Hi @HannahNg, Thanks for the question! You’ve identified the statement important to figuring out the answer choice here: “If and only if the landfill’s capacity to hold liquids is exceeded does the leachate escape into the environment.” This is a biconditional: the “if and only if” means that we diagram this with arrows in both directions, like the following: Landfill’s liquid capacity exceeded <—> Leachate escapes into the environment Which means that if either one happens, the other happens. However, it also means that if either one doesn’t happen, the other one doesn’t happen. In other words, we also know that ~Landfill’s liquid capacity exceeded <—> ~Leachate escapes into the environment And (E) gives us part of this conditional logic. (E) tells us ~Leachate escapes —> ~Landfill’s liquid capacity exceeded And this is a statement that directly follows from the biconditional. Thus, (E) is the correct answer. Hope this helps! Feel free to ask any other questions that you might have.