: Often hosts downloadable courseware for the Boya series, including the 2nd Edition workbooks.
: Check the back of the physical book or look for a separate teacher's manual PDF, as workbooks often don't include keys in the main body.
If all else fails, remember that the goal is to learn Chinese, not to wrestle with technology. Photocopy a friend’s workbook, use an audio recorder for listening sections, and keep practicing.