物体在运动过程中,克服重力做功50J,则 A.物体的重力势能可能不变 B.物体的

题型:选择题

问题:

物体在运动过程中,克服重力做功50J,则

A.物体的重力势能可能不变

B.物体的重力势能一定减小50J

C.物体的重力势能一定增加50J

D.物体的重力一定做功50J

考点:重力势能
题型:选择题

一般来说,长期理财规划建议书应包含的假设前提有( )a 国内政治 经济环境将不会有重大改变b 经济增长率 通货膨胀率 利率 汇率和税率的变动趋势c 工资增长水平 未来消费支出的变动趋势d 无其他人力不可抗因素和不可预见因素的重大不利影响

A.abcd

B.bcd

C.abd

D.cd

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从基因和病因学出发,我国将心肌病分类为()

A.家族/遗传性

B.混合性

C.病毒/免疫性

D.非家族性/获得性

E.特发性

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为了计算导电材料在不同温度下的电阻值,我们把温度每升高1℃时,导体电阻值的增加与原来电阻值的比值叫做导体电阻的温度系数,用“a”表示。

题型:选择题

简述完整工业投资项目的现金流量的内容

题型:选择题

Immigrants are consumers as well as producers, so they create jobs as well as taking them. And the work they do need not be at the expense of native workers. Immigrants often hold jobs that natives are unwilling to accept at any feasible wage.

Also, immigrants sometimes help to keep industries viable (能存活的) that would otherwise disappear altogether, causing employment to fall. This was the conclusion of a study of the Los Angeles garment industry in the 1970s and 1980s. And when immigrants working for low wages do put downward pressure on natives’ wages, they may raise the (real) wages of natives in general by keeping prices lower than they otherwise would be.

In theory, then, the net effect of immigration on native wages is uncertain. Unfortunately, most of the empirical (经验主义的) research on whether immigrants make natives worse off in practice is also inconclusive except the effect, one way or the other, seems small. Most of this research has been done in America: if there were any marked influence on wages, that is where you would expect to find it, given the scale of immigration and the tendency of the newcomers to concentrate in certain areas. But most studies have compared wages and employment in areas with many immigrants to wages and employment in areas with few. For instance, one examined the impact of sudden and notorious inflow of refugees to Miami from the Cuban port of Mariel in 1980. Within the space of a few months, 125000 people had arrived, increasing Miami’s labor force by 7%. Yet the study concluded that wages and employment among the city’s natives, including the unskilled, were virtually unaffected. Another study examined the effect of immigration on wages and employment of those at the bottom of the jobs ladder-unskilled blacks and Hispanics. It found that a doubling of the rate of immigration had no detectable effect on natives.

The most recent work, admittedly, has tended to question these findings. Using more detailed statistics and more sophisticated methods than the earlier studies, this work has tended to find that immigrants’ wages take longer to rise to the level of the natives’ wages than has been supposed. This implies a more persistent downward pressure on the host economy’s labor market.

Typically these studies find that immigration does depress unskilled natives’ wages to a small extent. But nearly all economists would agree that the effects of immigration are insignificant in relation to other influences.

It is certain, according to empirical research, that ().

A. immigration has a positive effect on native wages

B. immigration makes unskilled blacks and Hispanics worse off

C. immigration has only a small effect on native wages

D. immigration has a marked influence on natives in areas with dense immigrant population

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