Now listen carefully and answer questions 31 to 40.

现在请仔细听，并回答第31至第40题。

Much of the world now lives in an industrial civilisation. But this has only become possible because we have the necessary natural resources.

世界上大部分地区现在生活在工业文明之中，但这只有在我们拥有必要的自然资源的情况下才成为可能。

There are three types of natural resource without which industry could not exist. One of these is metal – without that we'd have no machines and no transportation.

有三种自然资源，没有它们工业就无法存在。其中之一是金属——没有金属，我们就没有机器，也没有交通运输。

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

另一种是化石燃料，我们需要用它来驱动那些机器。

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

但还有第三种资源，对于用皮带、管道和减震器连接机器各部件至关重要，那就是橡胶。它现在被用于超过40,000种产品，从防水鞋到外科手套。

At present, we have two types of rubber in common use. One is natural rubber, which nearly all comes from the Pará rubber tree. This was originally native to Brazil, but is now cultivated on plantations in South-East Asia.

目前，我们常用的橡胶有两种。一种是天然橡胶，几乎全部来自巴拉橡胶树，这种树原产于巴西，但现在在东南亚的种植园中种植。

Recently, however, concern's been growing that supplies may soon be insufficient for the world's needs. So what exactly is limiting the supply of natural rubber?

然而，最近越来越多的人担忧供应可能很快无法满足世界需求。那么到底是什么限制了天然橡胶的供应？

Well, for one thing, rubber trees don't just spring up overnight. It can take eight to ten years for a tree to start producing rubber, so cultivating them's a slow process.

首先，橡胶树不会一夜之间就长成。一棵树可能需要八到十年才能开始产胶，所以种植过程很缓慢。

And this leads to another problem. 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.

这又引发了另一个问题。对于大多数农作物，农民不需要考虑太远的未来，所以他们可以轻松地改变种植的作物种类或数量，如果他们发现该作物的需求在上升或下降的话。

But if you have to plant eight or ten years ahead, that's much harder. And also the rubber tree's very choosy about where it grows.

但如果必须提前八到十年规划种植，那就困难得多了，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. The result is that it can't be grown in the northern or southern parts of the globe, only around the equator.

它需要适宜的温度、适量的降雨和适当的海拔——不能太高也不能太低。结果是它不能在地球的南北部种植，只能在赤道附近种植。

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. It's very labour-intensive.

另一个问题是，橡胶的提取方式基本上与几百年前相同，即用手工方式，在树干上割小口，放置小杯子收集乳胶（即橡胶汁）。这非常耗费劳动力。

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

而且限制供应的不仅仅是初始生产。对于水和玻璃等其他资源，我们用完后可以回收，但橡胶虽然也可以回收，却非常困难，这也减少了可用量。

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

在过去几年里，天然橡胶的供应出现了新的威胁。一个问题与以下事实有关：东南亚几乎所有的橡胶树都源自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. The most dangerous threat is a fungus, which destroyed large numbers of rubber trees in Brazil, and which could cause devastation to plantations worldwide.

这意味着这些树的遗传多样性非常低，这反过来使它们非常容易感染疾病。最危险的威胁是一种真菌，它曾在巴西摧毁了大量橡胶树，可能对全球的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的农民越来越多地转向种植棕榈油，这对他们来说更容易且利润更高。

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.

最后，近年来东南亚与世界其他地区一样，反复遭受极端天气的袭击，这种情况未来可能还会持续。

However, as well as using natural rubber, it's also possible to make rubber synthetically. This works very well for some purposes, for example, making engine parts, or silicone pots and pans used for cooking.

然而，除了使用天然橡胶，也可以合成制造橡胶。这对某些用途非常有效，例如制造发动机零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. 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.

但与天然橡胶相比，合成橡胶的强度差远了，这意味着它无法在其他产品中替代天然橡胶。例如，天然橡胶和合成橡胶的混合物虽然在汽车轮胎中效果很好，但只有天然橡胶才能承受飞机轮胎在起降时的极端速度。

So for some time, scientists have been looking for alternative sources of natural rubber. One that's been known about for some time seems initially to be a rather unlikely source. It's a wild plant with yellow flowers that we normally regard as a weed when we see it in our gardens.

因此，科学家们一直在寻找天然橡胶的替代来源。其中一种已被知晓一段时间的来源，起初看起来是一个不太可能的来源——它是一种开黄色花朵的野生植物，我们在花园里看到它时通常将其视为杂草。

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

但当它被拔起并将根部切开时，会发现其中含有橡胶。

Now, compared to the rubber tree, dandelions produce relatively small amounts of rubber, but unlike rubber trees, they're very adaptable. They'll grow in all sorts of places, and they don't need rich soil.

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，它们适应性很强，可以在各种地方生长，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.

因此，目前有几个项目正在调查将蒲公英用作橡胶来源的可能性。

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

另一种可能性是一种在墨西哥和德克萨斯州生长的沙漠灌木……