Penning, W.L., author
S.L. Van Looy, [Date of publication not identified]
Buku Teks
Doren, Carl van, author
World Publishing, 1948
Buku Teks
Higgins, Paul C.
SAGE Publ., 1985
Buku Teks
Higgins, Raymond A.
Edward Arnold, 1987
Buku Teks
Higgins, Alex
McGraw-Hill Book Company, Inc., 1945
Buku Teks