登录之后可查看解析

B is corrent. The requirement is to identify the definition of structural unemployment. Structural unemployment exists when aggregate demand is sufficient to provide full employment, but the distribution of the demand does not correspond precisely to the composition of the labor force. This form of unemployment arises when the required job skills or the geographic distribution of jobs changes.
A is incorrect because frictional unemployment results from imperfections in the labor market. It occurs when both jobs and workers to fill them are available.
C is incorrect because cyclical unemployment is caused by contractions of the economy.
D is incorrect because the business unemployment rate is not an economic term.