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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:-> There are certain animals that live high in the mountains...
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2 .at altitudes up above the tree line, where trees don't grow.
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3 .And moving around in this mountainous environment can be challenging,
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4 .because the mountain slopes can be very steep and rocky....
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5 .Besides that, there's often ice or snow, making these rocky slopes slippery-and dangerous.
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6 .So animals that live at high altitudes have special features that help them move around in this difficult, mountainous environment.
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第3段
1 .So, for one thing,
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2 .many mountain animals have strong muscles that help them climb up and down the steep slopes.
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3 .As they're moving around, looking for food, they have to climb up these really steep mountainsides, at a dramatic incline,
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4 .and get down again, too.
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5 .For many animals this would be a real problem,
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6 .requiring great strength, and balance.
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7 .Um, mountain goats, which live high up in the mountains in parts of North America...
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8 .mountain goats have a large, well-muscled chest and front-leg area,
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9 .and these big, developed muscles in this area help them pull themselves up these near-vertical slopes,
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10 .and balance in tight positions when climbing down.
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第4段
1 .Also, mountain animals often have specially adapted feet
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2 .that help them keep from slipping when they're walking over ice or rocks.
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3 .High-altitude mountain slopes can be very slippery, especially when there's snow or ice on them,
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4 .and it's a long way down if they fall,
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5 .so mountain animals need to have a safe, sure footing.
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6 .Take the bighorn sheep, for instance....
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7 .These sheep have special toes that move independently
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8 .so they can dig into the rock and ice.
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9 .And the back parts of their feet have special round, rubbery pads that help them grip the surface of the rock or ice,
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10 .to prevent sliding as they move around.
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