Salisbury, Harrison E.
Atheneum, 1965
Buku Teks SO
Marcucci, Luisa
Studio Books , 1960
Buku Referensi
Hoffman, Ross J.S.
Littlefield, Adams, 1958
Buku Teks SO
edited by Angel Flores
Dell Publishing, 1963
Buku Teks SO
Nicholas, David
Longman, 1992
Buku Teks SO