Bremer, Kare
Timber Press, 1994
Buku Teks SO
edited by S.T. Cowan and L.R. Hill
Cambridge University Press, 1978
Buku Referensi
Bauman, Robert W.
Pearson, 2017
Buku Teks
Jeffrey, Charles
Cambridge University Press, 1982
Buku Teks SO
Naik, V.N.
Tata McGraw-Hill , 1984
Buku Teks SO