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 need to come up with a question about the story that requires an understanding of the relationship described in the background paragraph. The generated question should not be answerable without both the background and story. Write a question about the story that requires a relationship in the background paragraph to answer. Check whether your question requires both the background paragraph and the story to answer. If your question can be answered by only one of these, try to rewrite your question so that it requires both. Note that "flipping" a word in the question can give rise to a new question where the answer will be different from the original question. Often, "flipping" a word gives rise to flipping the direction of the relationship, for example, from "increase" to "decrease."

Background Paragraph: Retinitis is inflammation of the retina in the eye, which can permanently damage the retina and lead to blindness. The retina is the part of your eye that is also known as the "sensing tissue." Retinitis may be caused by a number of different infectious agents. Retinitis, also called Retinitis pigmentosa, has a prevalence of one in every 2,500-7,000 people. This condition is one of the leading causes that leads to blindness in patients in the age range of 20–60 years old. 
Story: Local hospital has launched a program to check if a patient has Retinitis. Resident ophthalmologist David is in charge of this program. In the first day of the program he checked two patients, patient A and patient B. The test result showed that patient A had Retinitis, but patient B did not have Retinitis. Then next day 
David checked two other patients, patient C and patient D. Patient C was 40 years old, but patient D was 80 years old. He found both patient C and D had Retinitis.
For which patient Retinitis will be one of the leading causes of blindness, patient C or patient D?

Background Paragraph: Middle adulthood lasts from the mid-30s to the mid-60s. During this stage of life, many people raise a family and strive to attain career goals. They start showing physical signs of aging, such as wrinkles and gray hair. Typically, vision, strength and reaction time start declining. Diseases such as type 2 diabetes, cardiovascular or heart disease, and cancer are often diagnosed during this stage of life. These diseases are also the chief causes of death in middle adulthood. 
Story: Margaret is a mother currently in the middle adulthood stage of her life.  Margaret's daughter, Vanessa, hasn't reached middle adulthood yet, and is still a teenager. Both of them enjoy reading beauty and fashion magazines so they can find age-appropriate tips on how to improve their look.
Who is less likely to begin developing gray hair?

Background Paragraph: Apex predators affect prey species' population dynamics and populations of other predators, both in aquatic and in terrestrial ecosystems. Non-native predatory fish, for instance, have sometimes devastated formerly dominant predators. A lake manipulation study found that when the non-native smallmouth bass was removed, lake trout, the suppressed native apex predator, diversified its prey selection and increased its trophic level. As a terrestrial example, the badger, an apex predator, predates on and also competes with the hedgehog, a mesopredator, for food such as insects, small mammals, reptiles, amphibians and ground-nesting bird's eggs. Removal of badgers (in a trial investigating bovine tuberculosis) caused hedgehog densities to more than double. Predators that exert a top-down control on organisms in their community are often considered keystone species. Humans are not considered apex predators because their diets are typically diverse, although human trophic levels increase with consumption of meat. 
Story: Rob is a biologist who is interested in native species conservation. To that end, he conducted two studies, case A and case B. In case A, a non native apex predator C was introduced in formerly apex predator D's habitat. In case B, same non native apex predator C was removed from formerly apex predator D's habitat. He now needs to analyze the results of these studies.

In which case predator D's population would decrease, case A or case B?