雅思阅读模拟练习一篇_雅思英语阅读

雅思阅读模拟练习一篇

　　The African Bush Willow, which grows in South Africa, has been recognised as a medicinal plant by local tribespeople for many years. In the past, its roots were used as purgatives and its gum was used to treat sores and ulcers. Common along river banks in southern Africa, this plant has proved both hardy and prolific, It is one of the worlds fastest-growing trees and can grow one metre in height annually to a maximum of fourteen metres. To sustain this level of growth normally requires warmth, rich soil and abundant water. but even when these are in short supply, the African Bush Willow can survive. It is resistant to severe drought and even sustained periods of frost, and temperatures well below zero do not damage the tree.

　　Combretastin, the active ingredient in the bark, was originally isolated form the stems and branches in the 1970a by South African researcher, Dr Gordon Cragg. A massive seventy-seven kilogrammes of material was needed from the tree to produce just a few milligrams of the active ingredient. However, scientists have now been able to produce the drug synthetically. This type of manufacturing has meant that the drug can now be mass-produced and used much more widely in the treatment of cancer. Most cancers are caused by tumours, which create their own network of capillaries to supply the blood they need in order to grow. The effect of combretastin is to reduce the tumours ability to create these capillaries and thereby starve the tumour to death.

【雅思阅读模拟练习一篇】相关文章：

★ 雅思阅读全真模拟题：satisfactory education

★ 雅思阅读的图标题技巧

★ 雅思阅读考前必看—Great a Task

★ 雅思阅读考前必看—Volt farce