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: The mechanical advantage of a machine is the factor by which it changes the force applied to the machine. Many machines increase the force applied to them, and this is how they make work easier. Compound machines tend to have a greater mechanical advantage than simple machines. That’s because the mechanical advantage of a compound machine equals the product of the mechanical advantages of all its component simple machines. The greater the number of simple machines it contains, the greater its mechanical advantage tends to be. 
Story: David was studying the processes involved in a machine. He collected a simple machine. He tagged it as case A. To compare it with compound machines, he collected two compound machines, case B and case C. Case B is a compound machine with few simple machines. And, case C is a compound machine with many simple machines. 
Question: Would case C have greater or smaller mechanical advantage than case B?
[EX A]: greater.

[EX Q]: Background Paragraph: HIV , or human immunodeficiency virus, causes AIDS. AIDS stands for "acquired immune deficiency syndrome." It is a condition that causes death and does not have a known cure. AIDS usually develops 10 to 15 years after a person is first infected with HIV. The development of AIDS can be delayed with proper medicines. The delay can be well over 20 years with the right medicines. Today, individuals who acquire HIV after 50 years of age can expect to reach an average human life span. 
Story: The police arrested two homeless people. James was 35 and had been HIV positive for 20 years, and Bill, who was 54 and was not HIV positive. They booked them and let them go. 
Question: Which person didn't have to take medicines to slow down the virus?
[EX A]: Bill.

[EX Q]: Background Paragraph: Surface temperature differences in turn cause pressure differences. A hot surface warms the air above it causing it to expand and lower the density and the resulting surface air pressure. The resulting horizontal pressure gradient moves the air from higher to lower pressure regions, creating a wind, and the Earth's rotation then causes deflection of this air flow due to the Coriolis effect. The simple systems thus formed can then display emergent behaviour to produce more complex systems and thus other weather phenomena.  Large scale examples include the Hadley cell while a smaller scale example would be coastal breezes. 
Story: In Steve's kitchen, there are two burners. Burner A is currently not turned on, and burner B is set to "medium." Steve was planning on cooking some fried eggs for lunch, but is currently distracted by an article in the newspaper that was deliver to his door. 
Question: Is the air above burner B more or less dense than the air above burner A?
[EX A]:
less.