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.
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Question: Background Paragraph: Turner et al (2006) derived crash prediction models for this report’s predecessor and found a
pronounced ‘safety in numbers’ effect in the models. Using the crash prediction model for mid-block
locations, generic motorist and cyclist volumes can be used to demonstrate the impacts on the
expected crash rate of varying motor vehicle and cycle volumes. As shown in figure 2.20, an increase
in the proportion of cyclists to the overall traffic volume causes an increase in expected crashes at
mid-block locations, but the crash rate increases at a decreasing rate. That is to say, the crash rate per
cyclist goes down as the cycle volume increases. 
Story: There were a lot of motorcycles on Interstate 4 last week. On Saturday, there were 1500 motorcyclists. On Sunday, there were 2500 motorcyclists. On Monday, there were 3500 motorcyclists. On Tuesday, there were 4500 motorcyclists. On Wednesday, there were 5500 motorcyclists. On Thursday, there were 6500 motorcyclists. On Friday, there were 7500 motorcyclists. 
Question: What day had a lower crash rate per cyclist: Sunday or Friday?

Answer: Friday.


Question: Background Paragraph: There was no additional air in the tire the second time Lawrence checked the air pressure, but something did change between the two measurements. The tires had rolled over 10 miles of road on the trip to school. Any time one surface moves over another, it causes friction. Friction is a force that opposes the motion of two surfaces that are touching, and friction between two surfaces always generates heat. Quickly rub your hands together and you’ll feel the heat generated by the friction between them. As the tires moved over the road, friction between the tires and road generated heat. In short, the tires got warmer and so did the air inside them. 
Story: There was a carnival game at the fair that allowed you to win a basketball if you could correctly guess which of the two balls had spun around a circular track more times. Each ball would be dropped into identical circular tracks and then a curtain would cover them. Ball A would then spin around the track a certain amount of times, and Ball B would spin around a certain amount of times. After they were done spinning, you had to guess which ball completed more revolutions. A boy came up and had no idea how to figure out the answer, but when he picked them up he noticed that Ball A was slightly warmer than Ball B. 
Question: Which ball completed more revolutions?

Answer: Ball A.


Question: Background Paragraph: In the U.S., the majority of electricity is produced by burning coal or other fossil fuels. This causes air pollution, acid rain, and global warming. Fossil fuels are also limited and may eventually run out. Like fossil fuels, radioactive elements are limited. In fact, they are relatively rare, so they could run out sooner rather than later. On the other hand, nuclear fission does not release air pollution or cause the other environmental problems associated with burning fossil fuels. This is the major advantage of using nuclear fission as a source of energy. 
Story: Iran an Iraq are 2 neighbors. Iraq produces its electricity by burning fossil fuels, while Iran uses nuclear fission as its energy source. 
Question: Which country causes more acid rain?

Answer:
Iraq.