Question

Which structure of a protein is the second folding of the protein chain ?

Answer 1

A tertiary structure is a protein that has changed from a secondary structure (example; helixes) to fold on itself, which is what I think you mean by the second folding. I'm assuming the first folding would be what is meant by the polypeptide chain forming (primary structure) folding into the secondary structure. 

I would go with tertiary. 

Answer 2

Im going to say the answer is C:)