A、CErtAin spirAl stAirCAsE is DEsignED so thAt EACh stEp AFtEr thE First onE is turnED 20°CountErCloCkwisE From thE onE immEDiAtEly BElow it，how mAny oF thE stEps mAkE up
ComplEtE rEvolutions
A、18 B、36
C、38
D、45 E、50