Helgren, D. M., & Sager, R. J. (1995). World geography today. Holt, Rinehart and Winston.
芝加哥风格引文Helgren, David M., 与 Robert J. Sager. World Geography Today. Austin, TX: Holt, Rinehart and Winston, 1995.
MLA引文Helgren, David M., 与 Robert J. Sager. World Geography Today. Holt, Rinehart and Winston, 1995.
警告：这些引文格式不一定是100％准确.