You are given a background paragraph that describes one or more causal or qualitative relationships such as a relationship in economics or a scientific law and a story that makes use of the concepts or the relationship described in the provided paragraph. You are also given a question about the story that requires an understanding of the relationship described in the background paragraph and the story. You need to come up with an answer to the given question; the answer will be a span from either the question or the story. In order to correctly answer the given question, you need to understand the relationship mentioned in the background paragraph and should be able to use it to understand that in the story. Your answer can not consist of any word that is not mentioned in any of these: the background paragraph, the story, or the question. You can directly copy and paste a span from the story or the question while answering the given question.

[EX Q]: Background Paragraph: Iron is first oxidized to iron(II) ions by oxygen. In the second step, the iron(II) ions are further oxidized and combine with water and oxygen gas to produce a hydrated form of iron(III) oxide known as rust. Rusting is one of many example of corrosion. Corrosion is the deterioration of metals by redox processes. Corrosion causes enormous amounts of damage to buildings, bridges, ships, cars, and other objects. It has been estimated that corrosion costs the U.S. economy over 100 billion dollars each year. A great amount of time and effort is spent to try to limit or prevent corrosion. 
Story: Two neighboring cities had different climates. Dune city had very dry air and no rain, while Bay city had very high humidity, fog and lots of rain. 
Question: Which city had more problems with corrosion?
[EX A]: Bay.

[EX Q]: Background Paragraph: Before iodized salt was developed, some people experienced a number of developmental difficulties, including problems with thyroid gland function and mental retardation. In the 1920s, we learned that these conditions could usually be treated easily with the addition of iodide anion to the diet. One easy way to increase iodide intake was to add the anion to table salt. This simple step greatly enhanced health and development. Large amounts of iodide ion are also found in seaweed such as kelp (see picture above) and saltwater fish. 
Story: People from two villages ate lots of salt. People from Salt village used regular salt, while people from Sand village people used iodized salt in their diets, after talking to specialists. 
Question: Which village had more people experience developmental difficulties?
[EX A]: Salt.

[EX Q]: Background Paragraph: Compared to conventional milk production, organic milk production tends to have lower eutrophication potential per ton of milk or per hectare of farmland, because it potentially reduces leaching of nitrates (NO3−) and phosphates (PO4−) due to lower fertilizer application rates. Because organic milk production reduces pesticides utilization, it increases land use per ton of milk due to decreased crop yields per hectare. Mainly due to the lower level of concentrates given to cows in organic herds, organic dairy farms generally produce less milk per cow than conventional dairy farms. Because of the increased use of roughage and the, on-average, lower milk production level per cow, some research has connected organic milk production with increases in the emission of methane.Animal welfare issues vary among dairy farms and are not necessarily related to the way of producing milk (organically or conventionally). 
Story: Robert and his brother Dale are both dairy farmers that primarily produce milk products. Both Robert and Dale have farms that approximately the same size. Dale prefers to produce milk conventionally, as he likes the way that conventional milk tastes. Robert, on the other hand, decided to switch to organic milk production after reading an article online about it. 
Question: Whose farm, Robert's or Dale's, will have lower eutrophication potential?
[EX A]:
Robert's.