USSR, [date of publication not identified]
Buku Teks
Moscow: Novosti Press, 1977,
Buku Referensi
Pokshishevsky, V., author
Progress, 1974
Buku Teks
Graham, Loren R., author
Cambridge University Press, 1993
Buku Teks
Zvorykin, A.A., author
UNESCO, 1977
Buku Teks