若有理数a与3互为倒数，则a的值是（ ） A．3 B．13 C．-3 D．-13

关于摩擦力的下列说法中正确的是（　　）

A．相互挤压的粗糙物体间一定产生摩擦力

B．只有静止的物体才可能受到静摩擦力，只有运动的物体才有可能受到滑动摩擦力

C．一个物体在另一个物体表面滑动时，一定受到摩擦力作用

D．摩擦力可以是阻力也可以是动力

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, reports 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 newspapers.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 outsintosmany 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 their very 13 .Newspapers are sold at a price that 14 even a small fraction of the cost ofproduction.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, country, state, nation, and world—and even outer space. 1.A.Just when B.While C.Soon after D.Before

2.A.to give B.giving C.given D.being given

3.A.gather B.spread C.carry D.bring

4.A.reason B.cause C.problem D.purpose

5.A.make B.publish C.know D.write

6.A.another B.other C.one another D.the other

7.A.However B.And C.Therefore D.So

8.A.value B.ratio C.rate D.speed

9.A.spread B.passed C.printed D.completed

10.A.inform B.be informed C.to be informed D.informed

11.A.entertain B.encourage C.educate D.edit

12.A.on B.through C.with D.of

13.A.forms B.existence C.contents D.purpose

14.A.tries to cover B.manages to coverC.fails to cover D.succeeds in

15.A.source B.origin C.course D.finance

16.A.way B.means C.chance D.success

17.A.measures B.measured C.Is measured D.was measured

18.A.somewhat B.little C.much D.something

19.A.offering B.offered C.which offered D.to be offered

20.A.by B.with C.at D.about

下列因素能引起癌变的有（）

①电离辐射

②X射线

③过氧化氢

④紫外线

⑤苯

⑥肿瘤病毒

⑦碘液

⑧砷

⑨醋酸

A.①②③⑦⑧⑨

B.③④⑤⑥⑦⑧

C.①②④⑤⑥⑧

D.③⑤⑥⑦⑧⑨

RouterA上的路由表如图17-12所示，请在(9)～(12)空白处填写恰当的内容。

（12）处填（）

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