Richards, Jack C.
Cambridge University Press, 1985
Buku Teks SO
Nunan, David
Pearson Education, 2000
Buku Referensi
Moulton, William G.
Modern Language Association of America, 1966
Buku Teks SO
Gebhard, Jerry G.
Cambridge University Press, 1999
Buku Teks SO
Halliday, M.A.K.
Longman, 1966
Buku Teks SO