Murdock, George Peter, author
McGraw-Hill, 1959
Buku Teks
International Office , 1974
Buku Teks
Sova, Milos
StaÌtni PedagogickeÌ Nakladatelstvi, 1962.
Buku Teks
Cowles, Virginia, author
Harper and Brothers, 1953
Buku Teks
Churchill Livingstone, 1996
Buku Referensi