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Ans: (a) Insulin.Explanation: In 1983, Eli lily an american company, first prepared two DNA chains of human insulin.
In Recombinant DNA technology antibiotics are used (1) As selectable markers (2) To keep medium bacteria-free (3) to detect alien DNA (4) To impart disease-resistance to the host plant
The two polypeptides of human insulin are linked together by (a) covalent bond (b) disulphide bridges (c) hydrogen bonds (d) phosphodiester bond.