英语听力:自然百科 秋日黄石公园 Autumn—9(在线收听

 It cuts branches into more manageable lengths and then swims them down a network of purpose-built canals towards the dam. 

 
The pond to give this beaver protection from predators, and the canals allow it to forage far into the forest, carrying many times its own weight with ease. 
 
Autumn is the busiest time of year for beavers. It won’t be so easy to make repairs when the pond is frozen over.
 
The sound of running water is their stimulus to shore up gaps with timber and plug leaks with mud. 
 
But the dam not only serves the beavers. Moose come here from the forests around to feed on weeds that thrive in the beaver’s shallow pond. The weed is rich in vital sodium that the forest can’t easily provide.
 
But now that winter is approaching,another essential role for the dam is revealed. These smaller branches are not for fixing the dam, they are for eating.
 
The beaver secures them to the mud in the late autumn.
  原文地址:http://www.tingroom.com/lesson/zrbaike/2012/273771.html