Sadler, A. L.
Charles E. Tuttle, 1962
Buku Teks SO
Sansom, George Bailey, Sir, 1883-1965
Cresset Press, 1946
Buku Teks SO
Sadler, A. L.
Angus and Robertson, 1963
Buku Teks SO
Varley, H. Paul
Praegar Publisher , 1973
Buku Teks SO
Eto, Jun
International Society for Educationa Information, 1974
Buku Teks SO