According to Mankiw (2020), structural unemployment that arises from an above equilibrium wage is different from frictional unemployment because a) job search requires frictionally unemployed workers to "search" for jobs whereas an above equilibrium wage requires structurally unemployed workers to "wait" for jobs to open up O b) structurally unemployed workers originally earned more than frictionally unemployed workers O c) job search is shorter for structurally unemployed workers than frictionally unemployed workers