Frictional unemployment results from:（）

A. inflexible wages in the marketplace.

B. recessionary business conditions and inadequate aggregate demand for labor.

C. constant changes in the economy that prevent qualified unemployed workers from being immediately matched up with existing job openings.

调配麻醉中药的处方应留存

A．半年

B．1年

C．2年

D．3年

E．4年