阅读理解　　Crosby''s recent study of American historical demography is blithely based on the reconstitution of the records of single parishes, a method that often excludes migrants. Moreover, it is troublesome for historians to obtain information on the birthdates of people who relocated to the parish, and equally difficult to follow those who had migrated to new places of residence. Thus, the exclusion of migrants also followed from the way spatial units were once conceived by the parishioners themselves, a stable and unchanging pre-modern countryside of interchangeable towns unlike "modern" flows to cities. 　　As a result, migration was improperly assumed to be irrelevant because the small units in the countryside were interchangeable and migrants into a parish could thus stand as a proxy for those who had left. In any case, it was thought that migration in the countryside was repetitive and occurred only in response to life course events, such as finding a spouse, and thus, like the parishioners themselves, Crosby complacently equates the demographics of migrants to those of more sedimentary populations.

单选题 In the passage, the author is primarily concerned with________.

单选题 According to the passage, early American parishioners held which of the following views concerning parish demography?

A、 Migration between towns stands in direct contrast with the accumulation of population in cities.
B、 Parish populations would grow at fairly equal rates, given the fact that those who left a parish in response to life course events were usually replaced.
C、 Migration between parishes was a rare enough phenomenon that it was unnecessary to keep records of it in any fashion.
D、 Parish populations often chose to remain sedimentary as a result of the homogeneity of the various countryside parishes.
E、 Parish populations owed their existence on the whole to the influx of populations due to life course events.

单选题 According to the passage, Crosby has made which of the following assumptions concerning historical means of demography?

A、 Migration is in most cases dictated by life course events as opposed to the economic factors that contribute to the development of cities.
B、 Population growth tends not to affect the availability of proxies for replacing emigrants from population centers.
C、 Sedimentary populations are more historically significant than nomadic or migratory ones.
D、 It is permissible to rely upon a single source of information in studying population movement patterns.
E、 Migration can be disregarded as a demographic pattern in historical contexts prior to the development of large cities.

单选题 The passage suggests that one major difficulty in establishing patterns of migration is________.

A、 the infrequency of life course events, which restricts the amount of data available to demographers
B、 the overwhelming availability of proxies in migration patterns, which creates a degree of stasis in migration records
C、 the lack of parishioner birth records, which limits the hard evidence upon which demographers base their observations
D、 the homogeneity of single parishes, which makes it difficult to distinguish the motivations of migrants
E、 the repetitive nature of migration, which results in a surfeit of unusable data that overwhelms demographers