Empirically, Labour Market Segmentation Has Not Been Based Upon the Identification

Empirically, labour market segmentation has not been based upon the identification of which of the following?

A) When empirically identifying a priori occupational or industrial labour market segmentation, truncation bias results in which of the following?
B) a low skill sector with no on-the-job training
C) a high skill sector with limited employee mobility
D) non-economic barriers between sectors preventing mobility