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

Question: Oxide layer formed on the non-ferrous metal surface after its annealing is
[A].

removed by acid pickling.

[B].

hammered into the surface.

[C].

removed with coarse emery cloth.

[D].

left as such to protect the surface.

Answer: Option A

Explanation:

No answer description available for this question.