Downie, N. M.
Harper & Row, Pub., 1974
Buku Teks
Hibberd, R.G.
McGraw-Hill, 1969
Buku Teks
Ewer, J.R.
Longman, 1969
Buku Teks
Kraal, Edmund G. R.
Thomas Reed Publications, 1973
Buku Teks
Porter, Richard C.
Homewood, Ill. Richard D. Irwin 1982,
Buku Teks