Oxide layer formed on the non-ferrous metal surface after its annealing is__________________?

(A)  Hammered into the surface (X)
(B) Removed with coarse emery cloth (X)
(C) Removed by acid pickling ()
(D)  Left as such to protect the surface (X)

Answers: Oxide layer formed on the non-ferrous metal surface after its annealing is Removed by acid pickling.