Butterfiel, W. (1964). Effective personal letters (2nd rev.). Prentice Hall.
Chicago Style (17. basım) AtıfButterfiel, W. Effective Personal Letters. 2nd rev. Englewood Cliffs: Prentice Hall, 1964.
MLA (9th ed.) AtıfButterfiel, W. Effective Personal Letters. 2nd rev. Prentice Hall, 1964.
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