Overview6 copies each of all three reading levels, 18 books total. The world's population has risen to more than 7 billion people, making issues such as food supply, energy resources, and water quality even more serious. Population Growth examines this major issue in ways that emphasize the causes and effects of population growth. In addition, it examines why some countries face the challenge of a young population, while other countries must maintain the quality of life for an aging population. Finally, Population Growth explores the importance of education and economic opportunities in meeting these important challenges.