Answer:
They worked backwards from mRNA to DNA
Step-by-step explanation:
For people with the opposite answer options than the person who asked this question.
they found insulin producing genes in bacteria
they cloned insulin protein using pcr
they used the base sequence to find the amino acid sequence
they worked backwards from mrna to dna (this one is correct)
Don't be fooled by the other answers if your options aren't the same, look carefully. This is correct on ape x as of late May 2021. Good Luck!