With regard to insulin choose correct options.

(a) C-peptide is not present in mature insulin.

(b) The insulin produced by rDNA technology has C-peptide.

(c) The pro-insulin has C-peptide.

(d) A-peptide and B-peptide of insulin are interconnected by disulphide bridges.

Insulin is a protein hormone that is composed of two chains, an A-chain having $21$ amino acids and a B-chain having $30$ amino acids, linked together by disulphide bonds (S-S). Insulin is derived from a $74-$amino acid prohormone molecule called proinsulin having C-peptide and this is removed before the processing of mature insulin and during the production of recombinant insulin, the two chains were separately produced and then linked with each other. C-peptide is absent in mature insulin.