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.

Background Paragraph: The primary role of red blood cells in the circulatory system is to transport oxygen to the tissues. The actual carrier of oxygen molecules is the protein hemoglobin, which binds to the oxygen and moves it throughout the body, releasing it in areas where the concentration of dissolved oxygen is low. A certain mutation in the gene for hemoglobin causes a slight change in the structure of this crucial protein, resulting in a disease called sickle-cell anemia. For people with this mutation, the hemoglobin produced by their red blood cells has a tendency to clump together, distorting the shape of the red blood cells and giving rise to the crescent-shaped cells seen above. By understanding the changes in structure that are the underlying cause of this disease, we have developed various ways to treat and manage this illness. 
Story: Dan had two children: Karen which had sickle-cell anemia, and his son Bob, which was healthy. 
Question: Which child has a hemoglobin that clumps together?
Karen.

Background Paragraph: Active immunity can also result from immunization. Immunization is the deliberate exposure of a person to a pathogen in order to provoke an immune response and the formation of memory cells specific to that pathogen. The pathogen is often injected. However, only part of a pathogen, a weakened form of the pathogen, or a dead pathogen is typically used. This causes an immune response without making the immunized person sick. This is how you most likely became immune to measles, mumps, and chicken pox. 
Story: When Emily was 4 years old she came down with a case of the chicken pox. She is now 14 and her younger brother Victor has now caught the chicken pox from another child at school. Emily opts to stay home and take care of him. 
Question: Given Emily never had the chicken pox, will Emily now have an increased or decreased chance of getting chicken pox from her brother?
increased.

Background Paragraph: For an inclined plane, the input distance is the length of the sloping surface, and the output distance is the maximum height of the inclined plane. This was illustrated in Figure above . Because the sloping surface is always greater than the height of the inclined plane, the ideal mechanical advantage of an inclined plane is always greater than 1. An inclined plane with a longer sloping surface relative to its height has a gentler slope. An inclined plane with a gentler slope has a greater mechanical advantage and requires less input force to move an object to a higher elevation. 
Story: John works as a mechanical engineer in the auto industry. He is testing three surfaces, surface A, surface B, and surface C for their usability. Surface A has a gentler slope, surface B has a steeper slope, and surface C doesn't have any sloping. He needs to figure out advantages and disadvantages of each slope. 
Question: Which surface would not have mechanical advantage greater than 1, surface A or surface C?

surface C.