To solve this problem, we need to analyze each statement regarding insulin:$\newline \bullet$(a) C-peptide is not present in mature insulin.$\newline$ - Insulin is initially synthesized as a single polypeptide called preproinsulin.$\newline$ - It is then processed to proinsulin, which contains the A-chain, B-chain, and C-peptide.$\newline$ - During maturation, the C-peptide is removed, leaving only the A and B chains connected by disulphide bridges.$\newline$ - Therefore, statement (a) is correct.$\newline \bullet$(b) The insulin produced by rDNA technology has C-peptide.$\newline$ - Recombinant DNA technology typically produces mature insulin, which does not include the C-peptide.$\newline$ - Therefore, statement (b) is incorrect.$\newline \bullet$(c) The pro-insulin has C-peptide.$\newline$ - Pro-insulin is the precursor to insulin and includes the C-peptide.$\newline$ - Therefore, statement (c) is correct.$\newline \bullet$(d) A-peptide and B-peptide of insulin are interconnected by disulphide bridges.$\newline$ - In mature insulin, the A and B chains are connected by disulphide bridges.$\newline$ - Therefore, statement (d) is correct.$\newline$Now, let's identify the correct options:$\newline$Statements (a), (c), and (d) are correct.$\newline$This corresponds to Option 3: (a), (c), and (d) only.