throughout history man has changed his physical environment in order to improve his way of life. with the tools of technology he has altered many physical features of the earth.

　　he has transformed woodlands and prairies into farms and made lakes and reserviors out of rivers for irrigation purposes or hydroelectric power. man has also modified the face of the earth by draining marshes and cutting through mountains to build roads and railways.

　　however, man's changes to the physical environment have not always had beneficial results. today, pollution of the air and water is an increasing danger to the health of the planet. each day thousands of tons of gases come out of the exhausts of motor vehicles. smoke from factories pollutes the air of industrialized areas and the surrounding areas of the countryside. the pollution of water is equally harmful. the whole ecological balance of the sea is being changed and industrial wastes have already made many rivers lifeless.

　　now environmental protection is more pressing than ever before. as we know, massive destruction of environment has brought about negative effects and even poses a great threat to man's existence. indifference to these problems will mean committing suicide. therefore, effective measures should be taken and laws passed to conserve environment. otherwise,man is certain to suffer from the serious consequences caused by this lack of care for his living surroundings.