<qa>  What is the primary goal of this study?This primary objectives of this study are to compare the efficacy, safety, and tolerability of tenofovir disoproxil fumarate TDF versus adefovir dipivoxil ADV for the treatment of pre-core mutant chronic hepatitis B. Participants will receive TDF or ADV for 48 weeks double-blind. After 48 weeks, eligible participants switched to open-label TDF for up to 480 weeks. 