APA (7th ed.) Citation

Abbs, B., Sexton, M., & Clegg, J. Challenges: A multi-media project for learners of English. Longman.

Chicago Style (17th ed.) Citation

Abbs, Brian, Malcolm Sexton, and John Clegg. Challenges: A Multi-media Project for Learners of English. London: Longman.

MLA (9th ed.) Citation

Abbs, Brian, et al. Challenges: A Multi-media Project for Learners of English. Longman.