Cork is a light brown material harvested from the cork oak tree. Cork is lightweight, strong and resistant to water. 【小题1】 For thousands of years, people have used pieces of cork as closures for bottles because cork is made of small cells filled with air. It is said that no technology has been able to copy this unusual material exactly.

The cork oak tree is native to the western Mediterranean coast of Europe. 【小题2】 In fact, Portugal produces more than half of the world’s cork supply. Cork oak trees have to be at least twenty-five years old before they are ready for harvest. 【小题3】 Cork is gathered by skillfully cutting off the outer layer of the tree with special knives. The harvest weakens the tree temporarily, but it soon starts to grow a new layer of bark. Next, the cork harvest is set out in the open for six months. Then, the cork is boiled in order to clean it and make it softer. 【小题4】

Because cork oak trees are not killed during harvest, they can live for as long as 200 years. Also, used cork products can be recycled and used again. This makes cork a valuable renewable resource. 【小题5】Wine makers say cork stoppers in their bottles let the wine be aged and improve over time. But now some wine producers are changing to plastic or metal closures. Some environmentalists worry that if cork starts to lose its value, the cork oak forests in Europe will no longer be protected.