The structure of insulin consists of two polypeptide chains $A$ and $B$. These two polypeptide chains

• A
  Have equal number of amino acids
• B
  Chain $A$ has $21$ amino acids,while chain $B$ has $30$ amino acids
• C
  Chain $A$ has $30$ amino acids,while chain $B$ has $21$ amino acids
• D
  Chain $A$ has $11$ amino acids,while chain $B$ has $40$ amino acids