根据材料请回答 35～39 Population Densities The average population density(密度)of the world is 47 persons per square mile.Con-tinental densities range from no permanent inhabitants in Antarctica to 211 per square mile in Europe.In the western hemisphere, population densities range from about 4 per square mile in Canada to 675 per square mile in Puerto Rico.In Europe the range is from 4 per square mile in Iceland to 831 per square mile in the Netherlands. Within countries there are wide variations of population densities.For example, in E-gypt, the average is 55 persons per square mile, but 1,300 person inhabit each square mite in settled portions where the land is arable(适合耕种的). High population densities generally occur in regions of developed industrialization, such as the Netherlands, Belgium, and Great Britain, or where lands are intensively used for agriculture, as in Puerto Rico and Java.Low average population densities are charac-teristic of most underdeveloped countries. Low density of population is generally associated with a relatively low percentage of cultivated land.This generally results from poor quality lands.It may also be due to natu-ral obstacles to cultivation, such as deserts, mountains, or malaria-infested (疟疾横行的)jungles to land uses other than cultivation, as pasture and forested land； to primitive methods that limit cultivation to social obstacles. More' economically advanced countries of low population density have, as a rule, large proportions of their populations living in urban areas.Their rural population densities are usually very low.Poorly developed countries of correspondingly low population density, on the other hand, often have a concentration of rural population living on arable land, which is as great as the rural concentration found in the most densely populated industrial countries. 第 35 题 Along the banks of the Nile, we may expect to find