OPEN University of Sri Lanka <br/><br/>
Course of study leading to the degree of bachelor of science level 3 BTU 1201:pl 

 - 2nd ed. 
 - Nugegoda  The Open University of Sri Lanka  1995 
 - 96 p. 
<br/><br/><label>ISBN: </label>139135 
<br/><br/><label>Dewey Class. No.: </label>589.9  / OPE