Scott-Kilvert, Ian
John Webster
Longmans, Green, 1970
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Harrower, Elizabeth, 1928-
The watch tower
Angus & Robertson, 1966
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Merriam-Webster's guide to business correspondence : a merriam-webster
Merriam-Webster's, Incorporated, 1993
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Cornog, Mary Wood
Merriam-Webster?s vocabulary builder
Merriam-Webster Inc., 1994
 Buku Referensi
Bolander, Donald O.
The new Webster's spelling dictionary
Lexicon Publication, 1993
 Buku Referensi