英语听力：自然百科 秋日黄石公园 Autumn—8

 They may be a little safer here. But the food in the forest is far less nutritious¹ than on the riverbanks.  If they want to eat well and avoid wolves this winter, they'll need to keep on moving. As the elk² move gradually downwards³, they follow the rivers out of Yellowstone’s central plateau. 

 

The rivers in turn follow the path of glaciers⁴ that flowed from this great bowl in the last Ice Age, and carved their way right through the barrier of surrounding mountains. Today, these valleys are escape routes for animals from the returning ice of winter. 

 

Lower down, the valleys broaden, the rivers slow, and a richer variety of trees grows in the alluvial⁵ soils, the perfect home for Yellowstone’s most industrious⁶ creature. 

 

A beaver⁷ can fell a cottonwood tree in just a few hours, hundreds in a year. The beaver doesn't chew through the whole trunk, just enough to make the tree unstable⁸. It then retreats, and lets the wind do the rest.

 

1 nutritious   

adj.有营养的，营养价值高的

参考例句：

• Fresh vegetables are very nutritious.新鲜蔬菜富于营养。
• Hummingbirds have discovered that nectar and pollen are very nutritious.蜂鸟发现花蜜和花粉是很有营养的。

2 elk   

n.麋鹿

参考例句：

• I was close enough to the elk to hear its labored breathing.我离那头麋鹿非常近，能听见它吃力的呼吸声。
• The refuge contains the largest wintering population of elk in the world.这座庇护所有着世界上数量最大的冬季麋鹿群。

3 downwards   

adj./adv.向下的（地），下行的（地）

参考例句：

• He lay face downwards on his bed.他脸向下伏在床上。
• As the river flows downwards,it widens.这条河愈到下游愈宽。

4 glaciers   

冰河，冰川( glacier的名词复数 )

参考例句：

• Glaciers gouged out valleys from the hills. 冰川把丘陵地带冲出一条条山谷。
• It has ice and snow glaciers, rainforests and beautiful mountains. 既有冰川，又有雨林和秀丽的山峰。 来自英语晨读30分（高一）

5 alluvial   

adj.冲积的；淤积的

参考例句：

• Alluvial soils usually grow the best crops.淤积土壤通常能长出最好的庄稼。
• A usually triangular alluvial deposit at the mouth of a river.三角洲河口常见的三角形沉淀淤积地带。

6 industrious   

adj.勤劳的，刻苦的，奋发的

参考例句：

• If the tiller is industrious,the farmland is productive.人勤地不懒。
• She was an industrious and willing worker.她是个勤劳肯干的员工。

7 beaver   

n.海狸，河狸

参考例句：

• The hat is made of beaver.这顶帽子是海狸毛皮制的。
• A beaver is an animals with big front teeth.海狸是一种长着大门牙的动物。

8 unstable   

adj.不稳定的，易变的

参考例句：

• This bookcase is too unstable to hold so many books.这书橱很不结实，装不了这么多书。
• The patient's condition was unstable.那患者的病情不稳定。