Bowring, James R.
Prentice-Hall, 1960
Buku Teks
edited by Joan Davidson and Richard Lloyd
John Wiley & Sons, 1979
Buku Teks SO
Martin, Anne
Routledger Kegan Paul, 1958
Buku Teks
Hammonds, Carsie, 1894-
Mcgraw-Hill , 1950
Buku Teks
Moverley, John
Harper-Collins, 1986
Buku Teks SO