Furnivall, JS
Solidaridad publishing house, 1974
Buku Teks
Steinberg, David J. (David Joel), author
Westeriew Press, 1990
Buku Teks
Corpuz, Onofre D.
Prentice-Hall, 1965
Buku Teks
Steinberg, David J. (David Joel), author
Westview Press, 1994
Buku Teks
Castelo, Lea T.
Melencio M. Castelo, 1977
Buku Teks