Which statement is TRUE of muscle glycogen phosphorylase?

A、Itcatalyzesphosphorolysisofthe(α1-6)bondsatthebranchpointsofglycogen.;
B、Itdegradesglycogentoformglucose6-phosphate.;
C、Itexistsinanactive(a)formandaninactive(b)formthatisallostericallyregulatedbyAMP.;
D、Itremovesglucoseresiduesfromthereducingendsoftheglycogenchains.