There are many thoughts on the origins of civilization. One of the major factors involved was the increase in population. The development of techniques, primarily irrigation and flood control, which permitted agriculture in special areas such as the flood plain of the Tigris and Euphrates rivers, made possible the support of large population. Once populations reach a certain number, the older pattern of social organization breaks down and new ones develop. Specifically the older system, whereby each individual participated in food production and maintained a similar standard of living and whereby kinship(家属关系) served as the basic method of social organization, was replaced by the occupational division of labor, political and religious hierarchies(等级制度), public works such as road and public building construction, class systems, codes of law, markets, new forms of warfare, and urban centres. Allied with these important sociological traits are material traits, such as monumental architecture and the development of science and, in many cases, metallurgy(冶金学) and writing sustems. The earliest civilization, Sumer, developed in the Middle East. This was the Bronze Age of the Old World, during which people first developed the art of metallurgy, civilization also arose in other parts of the Old World, first in Eygpt, China, and India, and later in Europe and Africa. At this time, civilization also developed independently in the New World, in the Mexican area and in Peru and its adjacent(邻近的) areas. In the Old World the Bronze Age was followed by the Iron Age, which saw the rise and fall of great empires and the shift of power from the Middle East to Greece and Rome and then to Western Europe. In the 1700s the Industrial Age began, leading directly to the modern civilization of today. 46. The author of this passage __________________________________. A. gives a comparison between ancient civilization and modern civilization B. suggests that population increase is most important in the development of civilization C. tries to explain how civilization developed in human history D. explore the relation between agriculture and industry 47. According to the first paragraph, the increase in population _____________________. A. resulted in the development of agricultural technology B. resulted from the breakdown of old social organization C. caused the occupational division of labor D. was impossible without the development of agriculture 48. The word “traits” in Paragraph One most likely means ___________________________. A. main appearances                    B. great achievements C. distinguishing features                D. outstanding successes 49. Which of the following is NOT true according to the passage? A. The Bronze Age is one of the earliest civilizations. B. The Industrial Age started in the Middle East. C. The Bronze Age developed into the Iron Age. D. The use of metal instruments started from the Bronze Age. 50. Which of the following is NOT included in the expression “the Old World” used in the passage? A. American continent.                  B. Both Western and Eastern Europe. C. African continent.                    D. Asian countries.