Population Densities
The average population density (密度) of the world is 47 persons per square mile. Continental 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 Egypt, the average is 55 persons per square mile, but 1,300 person inhabit each square mile 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 characteristic 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 natural 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.
Which of the following area has the highest average population density?
A.Iceland.
B.Canada.
C.Puerto Rico.
D.Netherlands.
第4题
为明确诊断所需要做的检查首选
A.上消化道造影
B.腹部X线平片
C.腹部B超
D.钡灌肠
E.腹部CT
第5题
疑为结肠癌,检查首选
A.腹部透视
B.上消化道钡餐造影
C.钡剂灌肠
D.腹部CT
E.全消化道钡餐
第6题
疑为胃溃疡,检查首选
A.腹部透视
B.上消化道钡餐造影
C.钡剂灌肠
D.腹部CT
E.全消化道钡餐
第7题
为明确诊断进一步做哪项检查最有帮助
A.钡剂灌肠检查
B.胃肠道钡剂检查
C.腹部CT
D.结肠镜检查
E.腹部B超
第8题
疑为肠梗阻时,检查首选
A.腹部透视
B.上消化道钡餐造影
C.钡剂灌肠
D.腹部CT
E.全消化道钡餐
第9题
为明确诊断,应进行的检查是
A.X线钡剂灌肠检查
B.腹部B超
C.粪便检查
D.结肠镜
E.腹部CT
第10题
为明确诊断首选的检查是
A.诊断性腹腔穿刺
B.胃镜
C.腹部 B 超
D.腹部 CT
E.上消化道 X 线钡剂造影
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