This is a somewhat challenging question, in part because the editorial uses none of the usual premise or conclusion indicators to help us determine the structure of the argument. Nevertheless, you should realize that the last sentence supports immediately preceding claim, because it helps explain why railroad companies should not be held responsible for the accidents that occur at railroad crossings due to insufficiently large gates. The editorial’s argument, when reworded, is structured as follows:
Premise—A licensed driver is a capable adult who should know better.
Conclusion—Railroad companies are not responsible for the accidents that occur at railroad crossings.
Interestingly, the conclusion is worded as a rejection of an opposing argument (“some people claim that… but this is a mistake”). Take your time to understand precisely what the author means by that: if the opposing claim is a mistake, then railroad companies are not even partly responsible for the accidents that occur at railroad crossings.
The question stem asks us to identify a statement that, if assumed, would allow this conclusion to logically follow from the premises. Despite the word “assumed” in the stem, this is a Justify question because our job is not to identify a statement upon which the argument depends, but rather to prove the conclusion by adding a piece of information to the premises. The sufficient condition indicator (“if”) in the question stem is a reminder that you must select an answer that is sufficient to prove the conclusion.
As with most Justify questions, there is a logical gap between the premises and the conclusion. Just because the driver is a “capable adult” does not necessarily relieve the railroad company of any and all responsibility for the resulting accidents. The correct answer choice must state that it does in no uncertain terms: the drivers must be entirely to blame.
Answer choice (A): This answer choice strengthens the argument that the railroad companies can do little to prevent accidents at railroad crossings, but does not prove that such companies bear no responsibility whatsoever for the ensuing accidents. Some of the most attractive but incorrect, answer choices to Justify questions are those that strengthen, but do not prove, the conclusion.
Answer choice (B): As with answer choice (A), this one strengthens the position that railroad companies are not entirely at fault for the ensuring accidents, because capable adults should take measures to ensure their own safety. However, the editorial’s conclusion is that railroad companies are not even partly at fault. The mere fact that drivers share some of the responsibility does not relieve the railroad companies of all responsibility, which is what the editorial attempts to argue. Another Strengthen decoy.
Answer choice (C): This is the correct answer choice, as it puts the blame for the resulting accidents entirely on someone other than the railroad companies. If drivers are capable adults who disregard a clear warning of oncoming trains, then they are fully responsible for any resulting accidents. This answer choice immediately relieves the railroad company of any and all responsibility, justifying the editorial’s conclusion.
Answer choice (D): The fact that small children are not involved in the aforementioned accidents is certainly a relief, but it has nothing to do with the editorial’s argument.
Answer choice (E): This is an attractive answer choice, in part because it is worded so poorly. Take the double negative (“not unlimited”) and simplify it (“limited”). In a nutshell, answer choice (E) argues that the companies’ responsibility to promote public safety is limited. Limited responsibility, however, does not mean “no responsibility,” which is what the author is trying to argue. As with answer choices (A) and (B), this one strengthens the conclusion—but it does not prove it.