eli123, I'm not familiar what a business tax return is, (is the business a separate legal entity?) but in general I would assume that USCIS is most interested in your sponsor's individual taxes.
Form I-864 includes the following instructions:
If you checked box 22(b) (self-employed), you should have completed one of the following forms with your Federal income tax return: Schedule C (Profit or Loss from Business), Schedule D (Capital Gains), Schedule E (Supplemental Income or Loss) or Schedule F (Profit or Loss from Farming).You must include each and every Form 1040 Schedule, if any, that you filed with your Federal tax return.