Allen, W. Stannard <br/><br/>
Key to the exercises. 

 - 12th impr. 
 - London :  Longman,  1993 
 - 26 s.. ;  21 cm. 
<br/><br/><label>ISBN: </label>0582552044 
<br/><br/><label>Universal Decimal Class. No.: </label>8111.111