单项选择题
While the emergence and persistence of ethnic niches testify to the pervasive effects of social structures, the growing educational level of African Americans since the 1970s has also equipped them for jobs that immigrants Line found hard to obtain. The proportion of African Americans workers whose limited schooling confines them to such jobs as apparel manufacturing or domestic work has declined. In particular, African Americans have found a niche in the public sector, a shift that may have diminished the effects of immigrant competition and put them in a position to absorb the positive effects associated with the population gains produced by immigration. Without formal educational credentials, it is difficult for the least-skilled African Americans to exploit the ethnic networks implanted in government employment, and thus they must find employment in an immigrant saturated market. As the public sector is now a declining enterprise, and more and more immigrants seek access to public-sector jobs, only alternative deserving of attention is the creation of more private-sector employment for African Americans with limited schooling.
Which of the following statements best summarizes a distinction mentioned in the passage between public-sector employment and those of private-sector employment’（） A、 Private-sector work involves a lesser degree of immigrant competition than public-sector work.
B、 A growing educational level has assisted African Americans find work in the private-sector more than it has done so in the public-sector.
C、 Immigrant population gains have benefited workers in the public-sector more than they have workers in the private-sector.
D、 Private-sector work often requires less in the way of educational credentials than public-sector work.
E、 The private-sector tends to contain stronger ethnic networks than the public sector.