Gee, Wilson
D. Appleton-Century Company, 1934
Buku Teks SO
edited by Monbusho
Maruzen, 1985
Buku Referensi
edited by Allan M. Cartter
American Council on Education, 1964
Buku Teks
Kent Ridge Association of Southeast Asian Institute of Higher Learning 1983, 1983
Buku Teks
The British Council,
Buku Referensi