Kaplan, Jeffrey P.
Prentice Hall International, 1995
Buku Teks SO
Jespersen, Otto
George Allen and Unwin, 1933
Buku Teks
Makkink, H.J.
Nijgh and Van Ditmar, 1951
Buku Teks SO
Parrot, Martin
Cambridge University Press, 2003
Buku Teks
Helling, Pam
[American Management Association, ], 1992
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