设NA为阿伏加德罗常数,下列说法正确的是: A.标准状况下,5.6L四氯化碳含有

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问题:

设NA为阿伏加德罗常数,下列说法正确的是:

A.标准状况下,5.6L四氯化碳含有的分子数为0.25NA 

B.标准状况下,22.4LCH4中含有的分子总数为5NA 

C.常温常压下,14g氮气含有的原子数为NA

D.标准状况下,铝跟盐酸溶液反应生成1mol氢气时,转移的电子数为NA

考点:阿伏加德罗定律
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用数学归纳法证明:当n为正奇数时,xn+yn能被x+y整除,第二步的假设应写成______.

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利润是指企业在一定会计期间的经营成果。利润包括收入减去费用后的净额、直接计入当期利润的利得和损失等。( )

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招标采购项目经理的基本权限不包括(  )。

A.财务决策权

B.项目团队的组建权

C.项目范围决定权

D.项目实施控制权

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经营进出口业务是()

A.对外开放的基本职能

B.对外经济援助的基本职能

C.对外贸易的基本职能

D.对外投资的基本职能

题型:选择题

With unemployment rising and housing costs still high, cities around the country are experiencing a new and sudden wave of homelessness. Shelters are overflowing, and more people this year are sleeping on floors in dingy social service centers, living in cars or spending nights on the streets.

In New York, Boston and other cities, homelessness is at record levels, a consequence of a faltering (摇晃的) economy that has crumbled even further after the Sept.11 attacks.

A survey by the U. S. Conference of Mayors released last week found that requests for emergency shelter in 27 cities had increased an average of 13 percent over last year. The report said the increases were 26 percent in Trenton; 25 percent in Kansas City, Mo.; 22 percent in Chicago; 20 percent in Denver; and 20 percent in New Orleans.

An unusual confluence of factors seems to be responsible for the surge. Housing prices, which soared in the expansion of the 1990’s, have not gone down, even though the economy has tumbled. A stream of layoffs has newly unemployed people taking low-wage jobs that might have otherwise gone to the poor. Benefits for welfare recipients are expiring under government-imposed deadlines. And charitable donations to programs that help the disadvantaged are down considerably, officials around the country said, because of the economy and the outpouring of donations for people affected by Sept.11.

"This is an unprecedented convergence (集中) of calamities (灾难), " said Xavier De Souza Briggs, an assistant professor of public policy at the John F. Kennedy School of Government at Harvard. "It’s really a crisis. "

More than half the cities surveyed by the mayors’ group reported that in the last year people had remained homeless longer, an average of six months.

There is no total number for the homeless nationwide. Experts said it was difficult to compare the situation with statistics in previous decades, because counting methods have improved. Yet, several experts said they believed that the increases reported by cities like Boston and Chicago reflected a national trend.

"My impression is there is more homelessness now than there was 20 years ago, " Gary Burtless, an economist at the Brookings Institution, said, adding that he believed that economic factors were not the sole explanation.

"I think that there must be a greater segment of our population that has tenuous connections to family and friends, and therefore has fewer resources to fall back on when something very bad happens like when they lose their job, " he said.

According to economist Gary Burtless, What factor accounts for the surge of homeless apart from the economic explanation().

A. Political.

B. Social.

C. Religious.

D. International.

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