If the data does not duplicate for C, then the only way I can think of to do this is to use a subreport. Put it in the Group Footer and suppress when the group is not 'B'. Lots of folks try to avoid subreports, but this is one of those circumstances where I think it's going to be necessary.
- Use the table(s) that you need to produce the data for C. Link based on the field for B.
- If the data may run more than one page and you need the C group header on every page, group on the linking field and turn on "Repeat Group Header on Every Page". Otherwise, put the group header information in the Report Header for the subreport.
-Dell