Gregg, Pauline
George G. Harrap, 1967
Buku Teks
A.G. Champion...[et al.]
Baltimore, Md., USA: Arnold, 1987
Buku Teks
Clapham, John, Sir
The Cambridge University Press, 1949
Buku Teks
edited by F. M. L. Thomson
Cambridge University Press, 1990
Buku Teks
edited by F. M. L. Thomson
Cambridge University Press, 1990
Buku Teks