Gaya APA

Hesser, D, T., Leach, S, S. (1987). Focus On Earth Science: Review and Reinforcement Guide . Columbus, Ohio: Merrill Publishing Company..

Gaya MLA

Hesser, Dale, T.., Leach, Susan, S.. "Focus On Earth Science: Review and Reinforcement Guide". Columbus, Ohio: Merrill Publishing Company., 1987. Text.