Genetically engineered human insulin is manufactured by the use of

The first biochemical to be produced commercially by microbial cloning and genetic engineering is:

Consider the following statements about therapeutic drugs:
$I$. The recombinant $DNA$ technology is used for the production of therapeutic drugs which are safe and effective.
$II$. It avoids unwanted immunological responses,commonly observed with similar products isolated from non-human sources.
$III$. About $30$ recombinant therapeutics have been approved for human use in the world,including India.
Which of the statements given above are correct?

Genetic engineering is connected with

Correct chronological order of the steps occurring during gene therapy are
$I$. Lymphocytes are obtained from the patients
$II$. Lymphocytes are transferred to the culture dishes
$III$. Lymphocytes are transfected with the normal $ADA$ genes
$IV$. The transfected cells are returned to the patients
The chronological order should be

The main challenge for the production of insulin using $rDNA$ techniques was getting insulin into its matured form using $........$ bonds.