Unit 2The objective of this book is to introduce engineering and science students to the interdisciplinary study of environmental problems: their causes, why they are of concern, and how we can control them.这本书的目的是使理工科的学生了解跨学科间的研究环境问题：它们的起因，为什么它们受到关注，以及我们怎样控制它们。Pollution can be defined as an undesirable change in the physical, chemical, or biological characteristics of the air, water, or land that can harmfully affect the health，survival，or activities of humans or other living organisms.
