Saving the earth（The First Period）

    concern about the protective ozone layer rose more recently when data from satellites and ground stations showed that ozone levels were dropping over areas other than antarctica.low ozone levels were recorded in the spring and summer over the united states and over other populated areas in the world.
    although many countries have already begun stopping the use or ozone—destroying
 chemicals, the new findings are expected to advance the timetable for a total ban of the chemicals.
2.pollution
people today all over the world are beginning to hear and learn more and more about tile problem of pollution.pollution is caused either by the release(排放)of completely new and often artificial substances into the environment, or by releasing greatly increased amounts of a natural substance.such as oil from oil tankers into the sea.with the development of modern industry，many of the goods and machines we need and use in our daily lives are creating a number of waste products which upset the environment balance.many of these waste products can be prevented if people pay more attention，but clearly while more and more new goods are  produced and  made complex，there will be new dangerous wastes to be thrown away，for example，the  waste products  from  nuclear power stations.many people，therefore, see pollution as only part of a larger and more complex problem.
   there is no doubt that much of the pollution caused could be controlled if only companies, individuals and government would make more efforts.in the home there is an obvious need to control litter and waste.food comes wrapped up three or four times in packages that all have to be got rid of；drinks are increasingly sold in bottles or times which cannot be reused.this not only causes a litter problem，but  also  is  a  great  waste  of  resources，in terms of glass，metals and paper.
advertising has helped this process by persuading many of us not only to buy things we neither want nor need.but also to throw away much of what we do buy.pollution and waste combine to be a problem everyone can help to solve by cutting unnecessary buying, over consumption and careless release of the products we use in our daily lives.
the first period
teaching aims：
1.train the students’ listening ability.
2.improve the studens’speaking ability by talking about nature ecology and the environment.
3.learn and master some useful expressions for supporting an opinion.