精选优质文档-倾情为你奉上Unit 1 Past and PresentSaving the Environment, Great changes have taken place in mnay places during the past few years.The changes have brought many benefits,and have also caused a lot of serious problems.There is air pollution everywhere.Fctories let out their waste gas without doing anything to it.The air is not clean any more.Some people pour the waste water into the rivers and lakes directly and the water is dirty now.Besides,people cut down too many trees and leav