Steel, Danielle
Sphere Books, 1985
Buku Teks SO
Leagogo, Liberto Antonio C.
Information, Publication and Public Affairs Office, 1998
Buku Referensi
Information,Publication and Public affairs Office University of the Philipines Manila, 1998,
Buku Referensi
Farrell, Jane
J.B. Lippincott, 1986
Buku Teks SO
Greenspan, Adam
Wolters Kluwer, 2015
Buku Teks SO