Official justification :
Solution: E
This is an Inference question. In isolation, the phrase in the question stem, “most strongly supported”, could hint at either a Strengthen question or an Inference question. However, when we take the stem in its entirety, the structure of the problem begins to unfold. Remember: premises always support conclusions. Thus, if the information in the answer choices supports the argument above, the answer choices must be premises and the conclusion is found in the argument (leading us to believe the problem is a Strengthen question.) On the other hand, if the information in the body of the question supports the answer choices below, the argument’s conclusion must be found in the answer choices (leading us to believe the problem is an Inference question.) Since the question stem indicates that the information “above” is supporting answer choices below, the answer choices must be potential conclusions. Since we are looking at an Inference question, our first line of defense is the “no new information” filter. Remember that valid conclusions must always (not just sometimes) be true, and therefore must be based entirely on the information found in the premises. Conclusions containing new information not found anywhere in the argument may or may not be true.
Answer choice “A” contains information we cannot prove. It tells us about how the zebra mussels came to be in the Great Lakes, as well as explains how the zebra mussels are supplanting native species. However, there is no information about either of these facts in the premises. Therefore, we cannot make a conclusion about something we don’t have information on. Answer choice “A” is not necessarily true.
Answer choice “B” contains information we cannot prove. It postulates what would happen to the cultured-pearl industry if the zebra mussels expanded into the Mississippi River and supplanted native species. However, there is no information about any of these facts in the premises. Therefore, we cannot make a conclusion about something we don’t have information on. Answer choice “B” is not necessarily true.
Answer choice “C” contains information we cannot prove. While the body of the question calls the zebra mussels a “nuisance” in the intake pipes of nuclear power plants and water plants, this does not mean that there is no mechanical way to remove the zebra mussels. (The zebra mussels could be a “nuisance” with or without a means of removing them.) The premises contain no information on the existence (or lack) of means for removing the mussels. Therefore, we cannot make a conclusion about something we don’t have information on. Answer choice “C” is not necessarily true.
Answer choice “D” contains information we cannot prove. While the premises talk about how zebra mussels feed on algae, the conclusion in “D” goes beyond what we know. It postulates that, in the absence of zebra mussels, the existing algae would clog the intake pipes of nuclear power plants and water plants. However, there is no information about any of these facts in the premises. Therefore, we cannot make a conclusion about something we don’t have information on. Answer choice “D” is not necessarily true.
Answer choice “E” correctly combines existing premises to provide a conclusion based solely on the given facts. We know from the problem that mussels remove hazardous waste from the water. If they remove the waste but do not transform it, the waste can be nowhere else but in the mussels. Therefore, the mussels contain hazardous waste. Some novice test takers might take exception with answer choice “E” because they feel the problem contains no information about whether the mussels transform hazardous waste – this seems like new information not contained in the premises. This is a subtle trap of the Testmaker. In difficult Inference questions, the Testmaker will often include conditional premises (for example, “if this is true…”, “if this happens…”, “if this condition is met…”). While we naturally should be wary of these statements because it seems like they are part of the conclusion – in fact, if we can find an answer that does not contain such conditional premises, such an answer may be even a stronger conclusion – adding conditional premises is a trick designed by the Testmaker to potentially hide the correct answer. We can treat such conditional premises as part of the facts leading up to the conclusion. The conclusion still needs to stand on its own; in other words, it cannot contain information about topics or facts not mentioned in the rest of the argument, but it can rely on the conditional premises hidden the answer choice.
