Chandler, Harold R.
BPC, 1970
Buku Teks
Nelkon, M.
Heineman Educational, 1962
Buku Teks SO
McKnight, Kent H.
"Minnesota: Burgess, 1968",
Buku Teks
Moon, Parker Thomas
Macmillan, 1926
Buku Referensi
edited by John A.S Read edited by
Singapore University Press for SEAMEO Regional Language Centre, 1984
Buku Teks SO