Final answer:
Mutation in the RNA dependent RNA polymerase of Hepatitis C is responsible for resistance to the drug sofosbuvir.
Step-by-step explanation:
Mutation in the RNA dependent RNA polymerase of Hepatitis C (HCV) is responsible for resistance to the drug sofosbuvir. Sofosbuvir is a nucleotide analog that interferes with the activity of the viral polymerase, preventing the replication of the HCV genome. The mutation in the RNA dependent RNA polymerase of HCV alters the structure of the enzyme, making it less susceptible to inhibition by sofosbuvir.