edited by James Flood, Julie M. Jensen, Diane Lapp, James R. Squire
Macmillan, 1991
Buku Referensi
edited by Merlin C. Wittrock; a project of the American Educational Research Association
Macmillan Library Reference USA, 1986
Buku Referensi
edited by Douglas A. Grouws
Macmillan Library Reference, 1992
Buku Referensi
Littlewood, William
Cambridge University Press, 1994
Buku Teks
Littlewood, William
Cambridge Uniiversity Press , 1983
Buku Teks