-. The world book encyclopedia, volume 21 (W.X.Y.Z). World Book, Inc.
Chicago Style (17th ed.) Citation-. The World Book Encyclopedia, Volume 21 (W.X.Y.Z). World Book, Inc.
MLA (8th ed.) Citation-. The World Book Encyclopedia, Volume 21 (W.X.Y.Z). World Book, Inc.
Warning: These citations may not always be 100% accurate.