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: A dilution effect is seen when animals living in a group "dilute" their risk of attack, each individual being just one of many in the group. George C. Williams and W.D. Hamilton proposed that group living evolved because it provides benefits to the individual rather than to the group as a whole, which becomes more conspicuous as it becomes larger. One common example is the shoaling of fish. Experiments provide direct evidence for the decrease in individual attack rate seen with group living, for example in Camargue horses in Southern France. The horse-fly often attacks these horses, sucking blood and carrying diseases. When the flies are most numerous, the horses gather in large groups, and individuals are indeed attacked less frequently. Water striders are insects that live on the surface of fresh water, and are attacked from beneath by predatory fish. Experiments varying the group size of the water striders showed that the attack rate per individual water strider decreases as group size increases. 
Story: Mike was visiting the African Savannah. One animal that interested him most was the African Buffalo. He noticed that the buffaloes would usually live in a large herd, often exceeding few hundreds. He noted that as case A. But sometimes the buffaloes would live in a small herd. He noted that as case B. Interestingly, there are incidents when an aggressive male buffalo would live by itself. He noted that as case C. 
Question: In which case the group would get more benefit as a whole, case A or case B?
case B.

Background Paragraph: Some individuals have a specific mutation in the primary sequence of their hemoglobin molecules that causes them to aggregate, resulting in a deformation of their red blood cells. This abnormality is genetic in nature. A person may inherit the gene from one parent and have sickle cell trait (only some of the hemoglobin is hemoglobin S), which is usually not life-threatening. Inheriting the gene from both parents will result in sickle cell disease, which is a very serious condition. 
Story: Doctors studied two groups of patients. Group W which had people with sickle cell disease, and group A which had normal people in it. 
Question: Which group had fewer individuals inheriting the gene from both parents ?
group A.

Background Paragraph: Cavitation is, in many cases, an undesirable occurrence. In devices such as propellers and pumps, cavitation causes a great deal of noise, damage to components, vibrations, and a loss of efficiency. Cavitation has also become a concern in the renewable energy sector as it may occur on the blade surface of tidal stream turbines.When the cavitation bubbles collapse, they force energetic liquid into very small volumes, thereby creating spots of high temperature and emitting shock waves, the latter of which are a source of noise. The noise created by cavitation is a particular problem for military submarines, as it increases the chances of being detected by passive sonar. 
Story: Stephanie and Barb are two friends that belong to a sailing club. They are having a lunch at the cafe in the club and discussing their latest boat purchases. Stephanie mentions that her latest boat she has been using has cavitation. Barb takes a bite of her sandwich and remarks that the boat she is currently using doesn't have any cavitation. 
Question: Whose boat will need repairs more frequently?

Stephanie.