St John, Maggie Jo
Prentice Hall ELT, 1994
Buku Teks
O`Guinn, Thomas C., author
CT Cengage Learning, 2015
Buku Teks
Belch, George F., author
McGraw-Hill, Irwin, 2001
Buku Teks
Hotchkiss, George Burton, author
Alexander Hamilton Institute , 1961
Buku Teks
White, Roderick, author
McGraw-Hill, 2000
Buku Teks