APA (7th ed.) Citation

Hawking, L., Hawking, S. W., Galfard, C., & Parsons, G. (2009). George's secret key to the universe. Simon & Schuster Books for Young Readers.

Chicago Style (17th ed.) Citation

Hawking, Lucy, S. W. Hawking, Christophe Galfard, and Garry Parsons. George's Secret Key to the Universe. New York: Simon & Schuster Books for Young Readers, 2009.

MLA (8th ed.) Citation

Hawking, Lucy, et al. George's Secret Key to the Universe. Simon & Schuster Books for Young Readers, 2009.

Warning: These citations may not always be 100% accurate.