Piyadasa, Geraldine R. <br/><br/>
Environmental Studies Book-4. 

 - 2nd Ed. 
 - Pannipitiya :  2004. 
 - 80 p. 
<br/><br/><label>ISBN: </label>9789553550422 
<br/><br/><label>Dewey Class. No.: </label>333.707  / PIY