Penalver, Rafael A.
Arco Publishing, 1984
Buku Teks SO
Penalver, Rafael A.
Arco Publishing, Inc., 1981
Buku Teks SO
editors, John M. Last, Robert B. Wallace ; associate editors, Elizabeth Barrett-Connor [and others]
Appleton & Lange, 1992
Buku Referensi
edited by Philip E. Sartwell
Meredith Publ., 1965
Buku Teks SO
Smillie, Wilson G.
Macmillan, 1963
Buku Teks SO