Once, they were made entirely of natural rubber.

以往，轮胎完然橡胶制成。

Until recently, sneakers used natural rubber for this process.

很长时间以来，在这个过程中，运动鞋的制作都是使用然橡胶。

But today, most outer soles are made with a synthetic blend of natural rubber and byproducts from coal and oil.

但是如今，大多数外底材料是然橡胶和煤及石油的副产品混合而成。

It is usually cheaper than natural rubber.

它然橡胶便宜。

Some of that will be natural rubber obtained from the sap of rubber trees.

其中一些将是从橡胶树的汁液中提取的然橡胶。

People get natural rubber from rubber trees as a white, milky liquid, which is called latex.

人们从橡胶树上获取然橡胶，呈白色乳状液体，称为乳胶。

Today, the world needs so much rubber that we use both natural and artificial rubber in large amounts.

今，世界需要如此多的橡胶，以至于我们大量使用然橡胶和人造橡胶。