APA (7th ed.) Citation
Hardach, G., Ross, P., & Ross, B. (1987). <The> First World War 1914-1918 (1. ed.). Penguin Books.
Chicago Style (17th ed.) Citation
Hardach, Gerd, Peter Ross, and Betty Ross. <The> First World War 1914-1918. 1. ed. Harmondsworth: Penguin Books, 1987.
MLA (9th ed.) Citation
Hardach, Gerd, et al. <The> First World War 1914-1918. 1. ed. Penguin Books, 1987.
Warning: These citations may not always be 100% accurate.