在无线传输介质中,无线传输的方式可分为( )。 A.地面微波 B.红外线传输 C.

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问题:

在无线传输介质中,无线传输的方式可分为( )。

A.地面微波

B.红外线传输

C.紫外线传输

D.卫星微波

考点:造价工程师建设工程技术与计量(安装)建设工程技术与计量(安装工程部分)
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计算下列各式,并且把结果化为只含有正整数指数幂的形式.
(1)(a2b-3-2⋅(a-2b32
(2)(x5y2z-3-2
(3)a-2b2•(-2a2b-2-2÷(a-4b2
(4)(
3
4
c2a-1b-3)
3
(2a2b-1c-1)3
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食管癌的细胞学普查未获得公认的主要原因()

A.筛查方法有一定痛苦

B.经费开支较大

C.假阳性较多

D.缺乏严格对照可降低死亡率的结果

E.早期发现率较低

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At the heart of the debate over illegal immigration lies one key question: are immigrants good or bad for the economy? The American public overwhelmingly thinks they’re bad. Yet the agreement among most economists is that immigration, both legal and illegal, provides a small net boost to the economy. Immigrants provide cheap labor, lower the prices of everything from farm produce to new homes, and leave consumers with a little more money in their pockets. So why is there such a discrepancy between the perception of immigrants’ impact on the economy and the reality?

There are a number of familiar theories. Some argue that people are anxious and feel threatened by an inflow of new workers. Others highlight the stress that undocumented immigrants place on public services, like schools, hospitals, and jails. Still others emphasize the role of race, arguing that foreigners add to the nation's fears and insecurities. There’s some truth to all these explanations, but they aren’t quite sufficient.

To get a better understanding of what’s going on, consider the way immigration’s impact is felt. Though its overall effect may be positive, its costs and benefits are distributed unevenly. David Card, an economist at UC Berkeley, notes that the ones who profit most directly from immigrants’ low-cost labor are businesses and employers —meatpacking plants in Nebraska, for instance, these producers’ savings probably translate into lower prices at the grocery store, but how many consumers make that mental connection at the checkout counter? As for the drawbacks of illegal immigration, these, too, are concentrated. Native low-skilled workers suffer most from the competition of foreign labor. According to a study by George Borjas, a Harvard economist, immigration has reduced the wages of American high-school dropouts by 9%. 

Among high-skilled, better-educated employees, however, opposition was strongest in states with both high numbers of immigrants and relatively generous social services. What worried them most, in other words, was the financial burden of immigration. That conclusion was reinforced by another finding: that their opposition appeared to soften when that financial burden decreased, as occurred with welfare reform in the 1990s, which curbed immigrants’ access to certain benefits.

The irony is that for all the overexcited debate, the net effect of immigration is minimal. Even for those most acutely affected — say, low-skilled workers, or California residents — the impact isn’t all that dramatic. “The unpleasant voices have tended to dominate our perceptions,” says Daniel Tichenor, a professor at the University of Oregon. “But when all those factors are put together and the economists calculate the numbers, it ends up being a net positive, but a small one.” Too bad most people don’t realize it. 

小题1:What can we learn from the first paragraph?

A.Whether immigrants are good or bad for the economy has been puzzling economists.

B.The American economy used to thrive on immigration but now it’s a different story.

C.The agreement among economists is that immigration should not be encouraged.

D.The general public thinks differently from most economists on the impact of immigration.小题2:What is the chief concern of native high-skilled, better-educated employees about the inflow of immigrants?

A.It may change the existing social structure.

B.It may pose a threat to their economic status.

C.It may decrease .their financial burden.

D.It may place a great pressure on the state budget.小题3:What is the irony about the debate over immigration?

A.Even economists can’t reach an agreement about its impact.

B.Those who are opposed to it turn out to benefit most from it.

C.People are making too big a fuss about something of small impact.

D.There is no essential difference between seemingly opposite opinions.小题4:Which of the following might be the best title of the passage?

A.A debate about whether to immigrate.

B.A debate about the impact of illegal immigrants.

C.The great impact of immigrants on the economy.

D.Opposition to illegal immigration.

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以美国南北战争为背景编写一个历史短剧(可以设想自己是短剧中的人物)

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网络通信协议是计算机网络的组成部分之一,它的主要作用是()

A.负责说明本地计算机的网络配置

B.负责协调本地计算机中的网络硬件与软件

C.规定网络中所有通信链路的性能要求

D.规定网络中计算机相互通信时需要共同遵守的规则和约定

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