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第1段
1 .<-NARRATOR:-> Listen to part of a lecture in a biology class.
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第2段
1 .<-FEMALE PROFESSOR:-> OK, so we've been talking about what most animals do when they need food-
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2 .they simply go out and look for it.
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3 .But some animals do something entirely different when they need food.
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4 .Surprising as it may sound,
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5 .some animals actually spend a great deal of time taking care of their own food source....
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6 .they cultivate it-
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7 .sort of the way human farmers would-
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8 .so it will keep growing until it is ready for them to use.
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第3段
1 .Let's start with an animal that cultivates plants.
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2 .There's a certain fish-uh, it's called a damselfish-
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3 .that likes to eat a special kind of seaweed.
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4 .So wherever a patch of this seaweed grows,
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5 .there will usually be damselfish swimming above and around it.
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6 .Now the fish are there to provide protection from other plants so the seaweed can grow and then regrow as the damselfish eat it.
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7 .For example, if other plants start growing over the seaweed, blocking sunlight,
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8 .the damselfish remove those plants by biting off the parts that are getting too tall.
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9 .So, by protecting the seaweed from being over run and damaged by other plants,
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10 .the damselfish always have a supply of food ready to use.
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第4段
1 .Now some animals don't cultivate plants-
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2 .they take care of other animals as a source of food.
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3 .Take ants, for instance.
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4 .There are some species of black ants that care for tiny insects called aphids.
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5 .These aphids produce a sweet liquid that the ants like to eat,
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6 .so ants guard the aphids from being eaten by other animals
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7 .and help feed the aphids.
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8 .In fact, sometimes the ants even carry aphid eggs back to their own nests and raise the young aphids there.
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9 .Then the aphids grow and produce this sweet liquid that the ants eat.
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10 .So the ants make use of the aphids as a reliable source of food.
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