Làm quen với giáo trình IELTS các bạn sẽ thấy đây là một bộ giáo trình hết sức dễ hiểu và có ích cho ta trong việc học tiếng anh một cách nhanh chóng. Sử dụng tiếng anh sao cho tốt luôn đòi hỏi chúng ta phải có thời gian ôn luyện thật lâu và vất vả. | RECORDING SCRIPT damp. In dry conditions it can last for decades. Metals take even longer obviously. Most like tin or iron can take anything between one and ten years . s But that doesn t apply to aluminium does it And 80 of soft-drink cans are made of aluminium. p No that s right. Aluminium s a special problem because it doesn t rust. So recycling is really the only answer. And another major problem is plastics. There are 80 different types for a start. Scientists think a typical item like a bottle could take a hundred years to decay. But as plastic has only been around for about a century we can only really guess. And the longest lasting of all is glass. We know from archaeological evidence that glass can survive for at least 4 000 years and who knows maybe longer s Thanks Peter. Now just to round off I wanted to say a word about some of the factors which can affect the process of biodegrading. One is temperature things decay more quickly when it s warm and more slowly in cool temperatures. Another factor is humidity. A moist environment speeds up decay. And the third is oxygen - that s a bit more difficult because some materials like oil need the presence of oxygen to break down while others don t. T OK. Good work both of you. Now are there any questions Unit 4 Focus on listening 2 Case study São Paulo Is everyone here Good well last week we talked about the astonishing growth of the world s cities if you remember and today I want to look at some of the reasons for this. What is it that draws people to leave their homes and families and move to big cities To answer this question. I m going to take Sào Paulo in Brazil as an example. First some basics. There s a fact sheet on Sào Paulo in your books but I think it s slightly out of date so let me give you the correct information and you can make any changes. OK Well the city dates back to the 16lh century - 1554 to be precise. By 1970 it had a population of million not quite a megacity but growing fast. 1
