Crystal, D. (2004). The Penguin book of facts. New York: Penguin Books.
Trích dẫn kiểu ChicagoCrystal, David. The Penguin Book of Facts. New York: Penguin Books, 2004.
Deismireacht MLACrystal, David. The Penguin Book of Facts. New York: Penguin Books, 2004.
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