问题 选择题

下列有关动脉的特点的叙述,正确的是(  )

A.管壁厚、弹性大、管内血流速度快

B.管壁厚、弹性小、管内血流速度快

C.管壁薄、弹性小,管内血流速度慢

D.管壁薄、弹性小,管内血流速度慢

答案

人体内的血管有动脉血管、静脉血管、毛细血管三种类型.其中动脉血管管壁厚,弹性最大,管腔较小,血流速度快,其功能为将血液从心脏输送到全身各处去;静脉血管管壁较薄,弹性较小,管腔大,血流速度慢,其功能为将血液从全身各处输送到心脏去;毛细血管管壁最薄,只有一层上皮细胞构成,管腔最小,只允许红细胞呈单行通过,血流速度极慢,数量最多,其功能为物质交换的场所.动脉血管、静脉血管、毛细血管的结构特点、血流速度如下表

故选A

单项选择题
单项选择题

Who won the World Cup 1994 football game What happened at the United Nations How did the critics like the new play (1) an event takes place, newspapers are on the streets (2) the details. Wherever anything happens in the world, reporters are on the spot to (3) the news.

Newspapers have one basic (4) , to get the news as quickly as possible from its source, from those who make it to those who want to (5) it.

Radio, telegraph, television, and (6) inventions brought competition for newspaper. So did the development of magazines and other means of communication. (7) , this competition merely spurred the newspapers on. They quickly made use of the newer and faster means of communication to improve the (8) and thus the efficiency of their own operations. Today more newspapers are (9) and read than ever before. Competition also led newspapers to branch out into many other fields. Besides keeping readers (10) of the latest news, today’s newspapers (11) and influence readers about politics and other important and serious matters. Newspapers influence readers’ economic choices (12) advertising. Most newspapers depend on advertising for very (13) .

Newspapers are sold at a price that (14) even a small fraction of the cost of production. The main (15) of income for most newspapers is commercial advertising. The (16) in selling advertising depends on a newspaper’s value to advertisers. This (17) in terms of circulation. How many people read the newspaper

Circulation depends (18) on the work of the circulation department and on the services or entertainment (19) in a newspaper’s pages. But for the most part, circulation depends on a newspaper’s value to readers as a source of information (20) the community, city, county, state, nation, and world—and even outer space.

12()

A.on

B.through

C.with

D.of