1. To develop some reading abilities.
2.To learn about the main information of the passage.
3.To develop the sense of environmental protection.
课前预习：
1.化石燃料 ______________ 2.副产品__________________
3.温室效应 ______________ 4.温室气体__________________
5.甲烷，沼气_______________ 6.自然现象__________________
7.发生; 造成________________ 8.大量的____________________
