edited by David Barton
Multilingual Matters, 1994
Buku Teks SO
John Hartley [and others]
Rinehart and Winston, 1962
Buku Teks SO
Veit, Richard
Pearson, 2001
Buku Teks SO
Charles E. Tutle Co.Inc, 1959,
Buku Referensi
Shidle, Norman G.
McGraw-Hill, 1951
Buku Teks SO