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For the past five million years,
在过去的500万年中
Arizona's Colorado River has eaten away at the desert sandstone to create a gigantic canyon.
亚利桑那州的科罗拉多河冲走了大量沙石，形成一个巨大深邃的峡谷
It's over a mile deep and at its widest, it's 1 7 miles across.
它的深度超过1英里，最宽的地方达17英里
The Grand Canyon. This river has cut the world's longest canyon system,
这就是大峡谷。这条河冲蚀出了世界上最长的峡谷系
a 1 ,000 mile scar clearly visible from space.
在太空中也能清楚地看到这条长达1000英里的沟壑
As rivers leave the mountains behind, they gradually warm and begin to support more life.
河流离开山区之后，河水渐渐变暖，养育的动物也多了起来。
Indian rivers are home to the world's most social otter.
印度河里住着世界上最具社会性的水獭
Smooth-coated otters form family groups up to 1 7 strong.
印度水獭的一个家族可多达17名成员
Group rubbing not only refreshes their coats, but strengthens social bonds.
集体“按摩”不仅能清洁它们的皮毛，也能增强群体内部团结
When it comes to fishing, there is real strength in numbers.
当它们去捕鱼时，群体合作能保证它们屡战屡胜。
