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.

[Q]: Background Paragraph: Protozoa generally feed by engulfing and digesting other organisms. As consumers, they have various roles in food chains and webs. Some are predators. They prey upon other single-celled organisms, such as bacteria. In fact, protozoa predators keep many bacterial populations in check. Other protozoa are herbivores. They graze on algae. Still others are decomposers. They consume dead organic matter. There are also parasitic protozoa that live in or on living hosts. For example, the protozoan that causes malaria lives inside a human host. For their part, protozoa are important food sources for many larger organisms, including insects and worms. 
Story: An astronaut has just landed on a new martian planet and encounters two different protozoa. The first protozoa he finds, protozoa X, is eating algae that is floating on top of water. The second protozoa, protozoa Y, is found eating bacteria. Upon further study, it is found that these are the only foods these two specific protozoa eat. 
Question: Which protozoa is a herbivore?
[A]: protozoa X.


[Q]: Background Paragraph: Something that is elastic can return to its original shape after being stretched or compressed. This property is called elasticity . As you stretch or compress an elastic material like a bungee cord, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force . The farther the material is stretched or compressed, the greater the elastic force becomes. As soon as the stretching or compressing force is released, elastic force causes the material to spring back to its original shape. You can watch a demonstration of elastic force at this URL:. 
Story: Andy is playing with a rubber band. He stretches the rubber band out as far as he can without breaking it. 
Question: Will the amount of force required to stretch the rubber band increase or decrease as he stretched it further?
[A]: increase.


[Q]: Background Paragraph: Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species . These are species that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a detrimental effect on the whole ecosystem. In this example, the wolves would be a keystone species. 
Story: Two teams studied two types of animals: team A studied predators, while team B studied grazers. They learned a lot from this experience. 
Question: Which team learned more about wolves?
[A]:
team A.