Which of the following companies started selling humulin in $1983$?

How many of the following statements are correct?
$(i)$ Mature insulin is made up of $A, B$ and $C$ peptides.
$(ii)$ Removal of $C$-peptide helps in the maturation of insulin.
$(iii)$ In mature insulin,$C$-peptide is present.
$(iv)$ In insulin,chains $A$ and $B$ are linked by disulphide bonds.

At present,about $X$ recombinant therapeutics have been approved for human use the world over. Out of these,$Y$ are being marketed in India.

Genetically engineered human insulin is prepared by using:

The disadvantage of using porcine insulin in diabetic patients is

How was insulin obtained before the advent of $rDNA$ technology? What were the problems encountered?