A.All"Add"channelsrequireuniformpowerlevels.
B.TheflexibilityofwavelengthsperOADMislimited.
C.Itiseasiertobalance"Pass-Through"and"Add"channels.
D.Thereislowerpass-throughlossusingmulti-channelOADMs.
E.Youcanextractasinglechannelwithoutdroppingotherchannels.