sentences:  The selection rule for the incident light polarized longitudinally to the zigzag ribbon axis is that formula_2 is odd, where formula_3 and formula_4 number the energy bands, while for the perpendicular polarization formula_5 is even.Intraband (intersubband) transitions between the conduction (valence) sub-bands are also allowed if formula_5 is even.For graphene nanoribbons with armchair edges the selection rule is formula_7.