Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 31 to 35.

A leading question among anthropologists is: what exactly led to the development of human cities? Basically, modern humans have existed on earth for over 100,000 years. Yet it is only in the last 8,000 years that they have begun to gather in significant numbers and form cities. Prior to that period, humans existed in small family or tribal groups, generally consisting of fewer than 100 individuals. What, then, led humans to make the dramatic shift from living in small groups to living in large, organized cities? It seems that the development of cities required a particular set of circumstances.

First, it required a minimum population density. For much of their early history, humans existed only in small numbers. This is due to the fact that early humans relied on hunting and gathering wild foods for their survival. Even the most fertile land would only support a relatively small number of predators, so it was not until humans began to practice agriculture that they were able to gather in large enough numbers to form cities.

Furthermore, the development of a city could only be possible if a large number of people shared a common language, culture and religion. Without such unifying factors, a cooperative, peaceful existence among large numbers of people would have been impossible.

Finally, it seems that early humans needed to be faced with a large problem, which one small group of individuals could not solve on its own. Only when large-scale cooperation was needed to overcome a problem would humans come together to form cities.