APA (7th ed.) Citation

Williams, M. L., Covington, B., & Paprock, K. (1999). Distance learning: The essential guide. Sage.

Chicago Style (17th ed.) Citation

Williams, Marcia L., Barbara Covington, and Kenneth Paprock. Distance Learning: The Essential Guide. Thousand Oaks, Calif: Sage, 1999.

MLA (9th ed.) Citation

Williams, Marcia L., et al. Distance Learning: The Essential Guide. Sage, 1999.