The correct option is B Getting insulin assembled into its mature form
The main challenge for production of insulin using rDNA technique was getting insulin assembled into its mature form. The primitive form of insulin called proinsulin contains the C peptide which is not a part of mature insulin. Therefore the scientists had to make the mature insulin using reverse transcriptase and the mature mRNA of the insulin gene. This method is known as cDNA technology, where complimentary DNA sequene of the mRNA is made and inserted as a gene of interest into the bacteria.