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: Parallel slowdown is a phenomenon in parallel computing where parallelization of a parallel algorithm beyond a certain point causes the program to run slower (take more time to run to completion).[1]

Parallel slowdown is typically the result of a communications bottleneck. As more processor nodes are added, each processing node spends progressively more time doing communication than useful processing. At some point, the communications overhead created by adding another processing node surpasses the increased processing power that node provides, and parallel slowdown occurs. 
Story: John landed a job as an IT manager. His boss asked him to figure out problems in two similar programs, program A and program B. John found program A having parallel slowdown, but program B does not have parallel slowdown. He has to weigh the merits of using these programs. 
Question: Which program is doing less useful processing, program A or program B?

Answer: program A.


Question: Background Paragraph: A person with a serious brain injury usually suffers permanent brain damage. These brain injuries usually occur when an external mechanical force, such as a violent blow or jolt to the head or body, causes brain dysfunction. An object penetrating the skull, such as a bullet or a shattered piece of the skull, also can cause traumatic brain injury. As a result, the person may have trouble talking or controlling body movements. Symptoms depend on what part of the brain was injured. Serious brain injuries can also cause personality changes and problems with mental abilities such as memory. Medicines, counseling, and other treatments may help people with serious brain injuries recover from, or at least learn to cope with, their disabilities. 
Story: Tammy and Rob rode a tandem bike down the hill. They hit a large rock and fell. Tammy wound up in the hospital and was diagnosed with a serious brain injury. Rob suffered only a mild concussion. 
Question: Which person had fewer problems with mental abilities?

Answer: Rob.


Question: Background Paragraph: Lactose intolerance is due to the lack of enzyme lactase in the small intestines to break lactose down into glucose and galactose.[3] There are four types: primary, secondary, developmental, and congenital.[1] Primary lactose intolerance occurs as the amount of lactase declines as people age.[1] Secondary lactose intolerance is due to injury to the small intestine such as from infection, celiac disease, inflammatory bowel disease, or other diseases.[1][4] Developmental lactose intolerance may occur in premature babies and usually improves over a short period of time.[1] Congenital lactose intolerance is an extremely rare genetic disorder in which little or no lactase is made from birth.[1]. 
Story: David works for a large pharmaceutical company as a research scientist. He has devised a procedure which can detect lactose intolerance in patients easily. To test his procedure he picked up four subjects form a large pool of sample. The four subjects are subject A, subject B, subject C, and subject D. Subject A has primary lactose intolerance; subject B has secondary lactose intolerance; subject C has developmental lactose intolerance; and subject D has congenital lactose intolerance. 
Question: Which subject has lactose intolerance due to genetic disorder, subject B or subject D?

Answer:
subject D.