Section B Directions: There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decide on the best choice. Each for its own reason, the study of residential mobility has been a concern of three disciplines: sociology, economics, and geography. For the economist, residential shifts provide a means for studying the housing and land markets. Geographers study mobility to understand the spatial distributions of population types. For the sociologist, interest in residential mobility has two sources: one stemming from the study of human ecology and the other, from a concern with the peculiar qualities of urban life. Of course, there are clearly overlapping concerns and it is often difficult to discern the disciplinary origins of a researcher by sole examining the kinds of questions he or she raises about mobility, although it is usually easier to identify a researcher's discipline by noting the methods used and the concepts employed. Urban mobility first appears in the sociological literature as a term expressing rather generalized qualities of urban, as opposed to the nonurban life. Some sociologists refer to the mobility of the city as the considerable sum of myriad and incessant sources of stimulation impinging upon the urban dweller, a sort of sensory overload which produces sophistication, indifference and a lowered level of affection in urban dwellers. There is simply so much to experience that the urban dweller's capacity is reduced to react in a“spontaneous” and“natural”way to urban existence. It is mobility in this sense that produces some of the special qualities of urban life which, on the other hand, appeals to migrants as an escape from the dullness and oppression of rural existence with its lack of change and stimulation, and on the other hand, produces anomie and alienation in a society where men see each other primarily as means to ends rather than as ends in themselves. Of course, mobility in this larger sense of sensory overload is not a concept which lends itself easily to measurement, especially since it is a macro-system property. Geographers who study mobility are most probably interested in______.