Browne, Glenn J.
Bowling Green State University, 1986
Buku Teks
edited by Ralph B. Winn
Littlefield, Adams, 1963
Buku Teks
Bartholomew, Paul C.
W.M.C. Brown, 1951
Buku Teks
Gellhorn, Walter
Macmillan, 1961
Buku Teks
Jensen, Merrill
Kriger, 1979
Buku Teks