OPEN Univeristy of Sri Lanka <br/><br/>
Course of study leading to the degree of bachelor of science, level 4- PSU 2115- 

 - Nugegoda  The Open University of Sri Lanka  1987 
 - 81 p. 
<br/><br/><label>ISBN: </label>123680 
<br/><br/><label>Dewey Class. No.: </label>541  / OPE