With regard to insulin,choose the 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.
Choose the correct answer from the options given below.

• A
  $(b)$ and $(d)$ only
• B
  $(b)$ and $(c)$ only
• C
  $(a), (c)$ and $(d)$ only
• D
  $(a)$ and $(d)$ only