APA (7th ed.) Citation

Duckworth, M., & Gude, K. (1999). Countdown to first certificate: Student's book. Oxford University Press.

Chicago Style (17th ed.) Citation

Duckworth, Michael, and Kathy Gude. Countdown to First Certificate: Student's Book. Oxford: Oxford University Press, 1999.

MLA (9th ed.) Citation

Duckworth, Michael, and Kathy Gude. Countdown to First Certificate: Student's Book. Oxford University Press, 1999.