Read the passage, then choose the correct answers.
No one knows the limits of population that the earth can support. Thomas Malthus, an English economist, developed a theory that became widely accepted in the nineteenth century. He suggested that because world population tended to increase more rapidly than the food supply, a continual strain was exerted upon available resources. Malthus cited wars, famines, epidemics, and other diseases as the usual limitations of population growth.