Vowels : J.P. Kelly and J.B. Heley
Majalah, Jurnal, Buletin
Hybels, Saundra, author
D. Van Nostrand, 1974
Buku Teks
Wresty Arief, author
Fakultas Kedokteran Universitas Indonesia, 2017
UI - Tugas Akhir
Brady, George S., author
McGraw-Hill, 1991
Buku Referensi
Brady, George S.
McGraw-Hill, 1979
Buku Referensi