The primary objectives of this study are: - To determine the efficacy of sofosbuvir (SOF)+ Ribavirin (RBV) for 16 or 24 weeks as measured by the proportion of subjects with sustained viral response 12 weeks after discontinuation of treatment (SVR12) - To determine the efficacy of SOF+RBV+pegylated interferon alfa 2a (PEG) for 12 weeks as measured by the proportion of subjects with SVR12 - To evaluate the safety and tolerability of all 3 treatment arms as assessed by review of the accumulated safety data