PART 4

第四部分。

You will hear part of a science lecture about different sources of rubber.

你将听到一段关于不同橡胶来源的科学讲座。

First, you have some time to look at questions 31 to 40.

首先，你有一些时间查看第31至40题。

Now listen carefully and answer questions 31 to 40.

现在请仔细听录音并回答第31至40题。

Much of the world now lives in an industrial civilisation.

当今世界上许多地区都生活在工业文明之中。

But this has only become possible because we have the necessary natural resources.

但这一切之所以成为可能，只是因为我们拥有必要的自然资源。

There are three types of natural resource without which industry could not exist.

有三类自然资源，没有它们，工业就不可能存在。

One of these is metal – without that we'd have no machines and no transportation.

其中之一是金属，没有金属，我们就不会有机器，也不会有交通运输。

Another is fossil fuels, which we need to power those machines.

另一类是化石燃料，我们需要它们来为这些机器提供动力。

But there's a third resource that's essential to connect the different parts of a machine together with belts and pipes and shock absorbers, and that is rubber.

但还有第三种资源，它对于用皮带、管道和减震器把机器的不同部件连接在一起至关重要，那就是橡胶。

It's now used in over 40, 000 products, from waterproof footwear to surgical gloves.

如今，橡胶被用于4万多种产品，从防水鞋到外科手套都有。

At present, we have two types of rubber in common use.

目前，我们常用的橡胶有两种。

One is natural rubber, which nearly all comes from the Pará rubber tree.

一种是天然橡胶，几乎全部来自帕拉橡胶树。

This was originally native to Brazil, but is now cultivated on plantations in South-East Asia.

这种树原产于巴西，但现在种植在东南亚的种植园里。

Recently, however, concern's been growing that supplies may soon be insufficient for the world's needs.

不过，最近人们越来越担心，橡胶供应可能很快就无法满足世界需求。

So what exactly is limiting the supply of natural rubber?

那么，究竟是什么限制了天然橡胶的供应呢？

Well, for one thing, rubber trees don't just spring up overnight.

首先，橡胶树并不是一夜之间就能长出来的。

It can take eight to ten years for a tree to start producing rubber, so cultivating them's a slow process.

一棵树需要八到十年才能开始产胶，所以培育橡胶树是一个缓慢的过程。

And this leads to another problem.

而这又带来了另一个问题。

With most crops, farmers don't have to think very far ahead, so they can easily change what crop they produce, or how much of a crop they produce, if they find the demand for that crop is rising or falling.

对大多数作物来说，农民不必提前考虑太久；如果发现某种作物的需求上升或下降，他们可以很容易地改变种什么，或改变产量。

But if you have to plant eight or ten years ahead, that's much harder.

但如果你必须提前八年或十年种下去，事情就要困难得多。

And also the rubber tree's very choosy about where it grows.

而且，橡胶树对生长环境非常挑剔。

It needs the right temperature, the right amount of rainfall, and the right altitude – not too high and not too low.

它需要合适的温度、适量的降雨和合适的海拔，既不能太高，也不能太低。

The result is that it can't be grown in the northern or southern parts of the globe, only around the equator.

结果就是，它不能种植在地球的北部或南部地区，只能在赤道附近生长。

Another problem is that the rubber is basically extracted in the same way as it's been done for hundreds of years, and that's by hand, by making small cuts in the trunk of the tree, and putting a little cup there to catch the latex, as the rubber is called.

另一个问题是，橡胶的提取方式基本上和几百年来一直采用的方法一样，也就是靠人工在树干上割开小口，再放一个小杯子接住流出的乳胶，也就是橡胶的原料。

It's very labour-intensive.

这非常依赖人工劳动。

And it's not just the initial production that's limiting supplies.

而且，限制供应的不只是最初的生产环节。

With other resources such as water and glass, when we've finished using them we can recycle them, but although this is also possible with rubber, it's very difficult, so that also reduces the amount we have available.

对于水和玻璃等其他资源，我们用完之后可以回收；橡胶虽然也可以回收，但非常困难，因此这也减少了我们可用的橡胶数量。

And in the last few years, there have been new threats to the supply of natural rubber.

近几年，天然橡胶的供应还面临了一些新的威胁。

One problem is linked to the fact that nearly all the rubber trees in South-East Asia are descended from just a small number of seeds brought from Brazil in the nineteenth century.

其中一个问题与这样一个事实有关：东南亚几乎所有橡胶树都源自19世纪从巴西带来的少量种子。

This means that there's very little genetic diversity among the trees, which in turn makes them very vulnerable to disease.

这意味着这些树之间的遗传多样性非常低，进而使它们极易受到疾病侵袭。

The most dangerous threat is a fungus, which destroyed large numbers of rubber trees in Brazil, and which could cause devastation to plantations worldwide.

最危险的威胁是一种真菌，它曾在巴西摧毁大量橡胶树，也可能给全球种植园造成毁灭性破坏。

Another problem is that farmers in South-East Asia are increasingly turning to the cultivation of palm oil, which is easier and more profitable for them.

另一个问题是，东南亚农民越来越多地转向种植油棕，因为这对他们来说更容易，也更有利可图。

And finally, in recent years South-East Asia, like other parts of the world, has been repeatedly hit by extreme types of weather, and this looks likely to continue in the future. However, as well as using natural rubber, it's also possible to make rubber synthetically.

最后，近年来东南亚和世界其他地区一样，反复遭受极端天气袭击，而且这种情况未来很可能还会持续。不过，除了使用天然橡胶，也可以人工合成橡胶。

This works very well for some purposes, for example, making engine parts, or silicone pots and pans used for cooking.

合成橡胶在某些用途上效果很好，比如制造发动机部件，或用于烹饪的硅胶锅具。

But compared with natural rubber, it's not anything like as strong, and this means it can't replace natural rubber in other products.

但与天然橡胶相比，它的强度远远不及，这意味着它无法在其他产品中替代天然橡胶。

For example, while a mixture of natural rubber and synthetic rubber works well in car tyres, only natural rubber can stand up to the extreme speeds of aircraft tyres during take-off and landing.

例如，天然橡胶和合成橡胶的混合物用于汽车轮胎效果不错，但飞机轮胎在起飞和降落时要承受极高速度，只有天然橡胶能够经受住这种考验。

So for some time, scientists have been looking for alternative sources of natural rubber.

因此，一段时间以来，科学家一直在寻找天然橡胶的替代来源。

One that's been known about for some time seems initially to be a rather unlikely source.

其中一种早已为人所知的来源，乍看起来似乎相当不可能。

It's a wild plant with yellow flowers that we normally regard as a weed when we see it in our gardens.

它是一种开黄色花的野生植物，我们平时在花园里看到它时，通常会把它当作杂草。

But when it's pulled up and its roots cut open, they're found to contain rubber.

但把它拔起来并切开根部时，人们发现里面含有橡胶。

Now, compared to the rubber tree, dandelions produce relatively small amounts of rubber, but unlike rubber trees, they're very adaptable.

与橡胶树相比，蒲公英产生的橡胶量相对较少，但与橡胶树不同的是，蒲公英适应性很强。

They'll grow in all sorts of places, and they don't need rich soil.

它们能在各种地方生长，而且不需要肥沃的土壤。

So at present there are several projects underway investigating the possibility of using dandelions as a source of rubber.

所以目前有几个项目正在进行，研究把蒲公英作为橡胶来源的可能性。

Another possibility is a desert shrub grown in Mexico and Texas …

另一种可能的来源是一种生长在墨西哥和得克萨斯的沙漠灌木……

That is the end of part 4.

第四部分到此结束。

You now have one minute to check your answers to part 4.

现在你有一分钟时间检查第四部分的答案。