听力原文

It's collected daily, bowl by bowl. It will be boiled and processed into one of the most important materials to a fast developing nation-rubber.
它每天都被采集，一碗又一碗。液体将被熬制成为一种非常重要的材料。橡胶对发展中国家来说尤为关键。
The expansion of the rubber forests began in the '50s when China, under a world rubber embargo, had to become self-sufficient in this vital product.
中国的橡胶林种植面积在五十年代时急速扩张，美国侵略朝鲜期间对当时的中国实行了全面的经济封锁和橡胶禁运。中国对这种战略原料的需求必须自给自足。
Beijing turned to the only place where rubber could grow, the tropical south of Yunnan.
北京当局把目光转向了橡胶树唯一能够快速成材的地方：位于热带地区的云南南部。
With efficiency and speed, some of the world's richest forests were torn up and burned. Replaced with mile upon mile of rubber plantation.
高效快捷的行动开始了，一些世间最丰茂的森林被摧毁并焚烧殆尽，取而代之的是成片的的橡胶林。
But there was a problem for the rubber growers. While Yunnan's unique natural forests can survive on the valley slopes which stretch to the north, just one severe frost will kill off these delicate rubber trees.
橡胶种植者的问题也接踵而至。尽管云南独特的天然林，能够在延伸到北部的山坡上茁壮成长，可是一场严峻的霜冻就能毁灭这片娇弱的橡胶林。

重点讲解

重点讲解：
1. self-sufficient
（国家或团体）自给自足的，自立的；
eg. This enabled the country to become self-sufficient in sugar.
这使得该国的食糖能自给自足。
eg. Using traditional methods poor farmers can be virtually self-sufficient.
采用传统的方法，贫穷的农民基本上能自给自足。
2. tear up
摧毁，拆毁，毁坏；
eg. Dozens of miles of railway track have been torn up.
好几十英里的铁轨被毁坏了。
eg. The company came under furious attack from environmentalists for tearing up the forests.
由于破坏了森林，这家公司受到环境保护主义者的猛烈抨击。
3. replace with
以…取代；以…接替；
eg. We've replaced the old adding machine with a computer.
我们用电脑取代了老式的加法计算器。
eg. Later, most executives reduce their need for celebrity and replace it with a desire for reputation.
在这以后，大部分经理减少了对出名的要求，代之以对声望的向往。
4. upon
用于名词叠用，表示数量多；
eg. Row upon row of women surged forwards.
一排排的女人涌上前去。
eg. I looked across the mountains, ridge upon ridge.
我放眼绵延起伏的群山。
5. kill off
全部杀死；灭绝；
eg. This spray will kill off any pests or insects.
这种喷雾能够消灭任何的害虫或者昆虫。
eg. These figures kill off any lingering hopes of an early economic recovery.
这些数字彻底扼杀了人们对经济早日复苏所抱的一线希望。