Callis, Helmut G.
Henry Holt and Company, 1959
Buku Teks
Joseph, Phillip, author
George Allen and Unwin, 1928
Buku Teks
Foreign Languages Press, 1963
Buku Teks
Pentony, DeVere E.
Chandler Pub. Co, 1962
Buku Teks
Keenan, George F., author
Harper & Row, 1964
Buku Teks