Butterfiel, W. (1964). Effective personal letters (2nd rev.). Prentice Hall.
芝加哥风格引文Butterfiel, W. Effective Personal Letters. 2nd rev. Englewood Cliffs: Prentice Hall, 1964.
MLA引文Butterfiel, W. Effective Personal Letters. 2nd rev. Prentice Hall, 1964.
警告：这些引文格式不一定是100％准确.