Brandt, Conrad
George Allen and Unwin, 1959
Buku Teks SO
Hirth, F.
The Statistical Department of The in Pectorate General of Customs, 1888
Buku Referensi
Isaacs, Harold R.
Standford University Press, 1951
Buku Teks SO
Ho Kan-Chih
Peking: Foreign Language Press, 1959
Buku Teks
Isaacs, Harold R.
Secker & Warburg, 1938
Buku Teks SO