Dange, Sindhu S.
      
      
         A anta Publications, 1984
       Buku Teks SO
   
Murphy, Gardner
      
      
         Basic Books, Inc., 1953
       Buku Teks SO
   
      
      
         Pearson Longman, 2008
       Buku Teks
   
Epstein, T. Scarlett
      
      
         Manchester University Press , 1962
       Buku Teks SO
   
Rosen, George
      
      
         University California Press, 1966
       Buku Teks