Artikel Jurnal
Allen, Edward David, author
Harcourt Brace Jovanovich, [Date of publication not identified]
Buku Teks
Harris, David P.
McGraw-Hill, 1969
Buku Teks
Stevick, Earl W.
Abingdon, 1967
Buku Teks
Pal, Saroj K.
Tata McGraw-Hill, 1982
Buku Teks