Cathodic protection involves supplying electrons to the metal to be protected from an external source. The external source maybe be an external（）or by（）

Cathodic protection involves supplying electrons to the metal to be protected from an external source. The external source maybe be an external（）or by（）
A.dc power source
B.Alternating Power Source
C.A Galvanic Couple
D.Cathode
正确答案：dc power source； A Galvanic Couple