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第1段
1 .Listen to part of a lecture from a biology class.
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2 .You’ve all seen pictures of polar bears, right?
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3 .Those are the giant white bears that live in the Arctic, up near the North Pole where it’s extremely cold and snowy for much of the year.
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4 . Well, as you can imagine polar bears have to spend a lot of time swimming around in the icy, cold water of the Arctic Ocean, so polar bears have developed certain bodily features, or adaptations that help them stay warm in the freezing Arctic environment.
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5 . Lets talk about a couple of these adaptations.
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6 .First, polar bears have an adaptation to help them hold in the heat of the sun.
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7 .As you know, dark colors absorb more sunlight than lighter colors do, so an animal living in the cold can stay warmer if the animal has dark coloring.
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8 .For example, even though polar bears have white fur, the skin underneath their fur is black, so when sunlight comes through the fur and hits their skin, the black skin absorbs a lot of light and heat from the sun and warms up their bodies.
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9 . Polar bears also have another adaptation against the cold.
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10 .This one prevents the cold water from reaching their skin.
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11 .As I said, they spend a lot of time swimming in icy water.
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12 . If that water got soaked into their fur, the fur wouldn’t be able to insulate the bears and keep them warm, so they have an adaptation that prevents that from happening.
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13 .For example, polar bears naturally have oily fur.
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14 .Yes, their fur actually has oil on it and this oil helps repel water and makes their fur waterproof.
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15 . In that way, the fur can continue to keep the bears warm even while they’re swimming.
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