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段落1

NARRATOR

Now listen to part of a lecture on the topic you just read about.

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段落2

FEMALE PROFESSOR

Sure, there’re some benefits to planting genetically modified trees, but are these trees really as great as they first sound?

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When you examine the subject closely, there are some serious problems and costs associated with using genetically modified trees.

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段落3

First, genetically modified trees may be resistant to one particular condition, but that doesn’t necessarily ensure their survival.

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Ya see, a typical nonmodified tree population is genetically diverse.

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That means that for most threatening conditions—poor climate, insects and other pests, whatever—there will be at least some individual trees of any given species of tree that are resistant.

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So even if most of one kind of tree are killed, those few resistant ones will survive and ensure the survival of that species of tree.

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But genetically modified trees are genetically much more uniform, so if they’re exposed to an environmental challenge they haven’t been designed for, they’ll all die.

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So if the climate changes or a… a new pest invades an area, the genetically modified trees will likely be completely wiped out.

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段落4

Now as to the second point, there are hidden costs associated with growing genetically modified trees.

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You see, the company that genetically modified the tree, tends to charge tree farmers much more for its seeds than unmodified tree seeds would cost.

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Also, after you’ve grown the tree, you can’t just collect the seeds and plant a new tree for free;

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by law, you have to pay the company every time you plant.

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段落5

And finally, genetically modified trees might actually cause even more damage to the local wild trees.

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You see, genetically modified trees often grow more aggressively than natural trees do, and genetically modified trees are typically planted among natural trees.

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As a result, the genetically modified trees outcompete the native trees for resources, sunlight, soil, nutrients, and water, eventually crowding out the natural trees.

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