The main difference is leadership: walkthroughs are led by the author, while inspections are led by a trained moderator (option C). Walkthroughs are informal meetings where the author guides peers through the document. Inspections are formal with defined roles - a trained moderator (not the author) leads, participants have specific responsibilities, and defects are systematically recorded. Option D is incorrect - authors can be present in inspections but don't lead them. Inspections are more rigorous and measurable.