APA (7th ed.) Citation

Boehm, R. G., Armstrong, D. G., & Hunkins, F. P. Geography: The world and its people.

Chicago Style (17th ed.) Citation

Boehm, Richard G., David G. Armstrong, and Francis P. Hunkins. Geography: The World and Its People.

MLA (8th ed.) Citation

Boehm, Richard G., et al. Geography: The World and Its People.