What is absent in mature insulin?

The disadvantage of using porcine insulin in diabetic patients is

$ELISA$ is based on:

Find the correct statements from the following:
$I.$ Gene therapy is a genetic engineering technique used to treat diseases at the molecular level.
$II.$ Calcitonin is a medically useful recombinant product in the treatment of infertility.
$III.$ Bt toxin is a biodegradable insecticide obtained from $Bacillus \text{ } thuringiensis$.

When a gene is targeted to correct a disease by amplifying the gene,what is this process called?

When and on whom was the first clinical gene therapy experiment performed?