单选题 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.

单选题 According to the passage, immigration will not threaten natives' benefits because ______.
A. they only take jobs created by immigrants
B. they often hold jobs that natives don't accept
C. they do not put downward pressure on natives' wages
D. they are unemployed most of the time

单选题 According to the Los Angeles study, immigrants ______.
A. sometimes help to maintain the existence of some industries
B. sometimes cause employment to fall
C. may lower the wages of natives in general
D. may help promote inflation

单选题 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

单选题 According to the most recent study, ______.
A. immigration only depresses unskilled natives' wages to a large extent
B. immigration puts a longer downward pressure on the natives' wages
C. immigrants' wages can rise to the level of natives' very quickly
D. immigrants tend to be in unemployment for a long time

单选题 The passage is intended to convey that the effect of immigration on natives' wages is ______.
A. uncertain B. persistent
C. inconclusive D. insignificant