Mann, Richard I.
Gateway Books, 1994
Buku Teks SO
Hopper, Melvyn A.
Eurasia Media, 1985.
Buku Teks SO
Indonesian Embassy, 1967
Buku Teks SO
[Publisher not identified], [Date of publication not identified]
Buku Teks
Hopper, Melvyn A.
Eurasia Media, 1985
Buku Teks