Ashford, Theodor Askounes
Holt, Rinehart and Winston, 1967
Buku Teks
Martin, Alfred N.
Lea & Febiger, 1993
Buku Teks
Winter, Stephen S.
Harper & Row, 1967
Buku Teks
Cambridge University Press, 2003
Buku Referensi
Potter Merle. C
Prentice-Hall, 1978
Buku Teks