Which of the following statements about the Robinson-Patman Act is true? a. The Robinson-Patman Act prohibits price discrimination within the United States unless price differences can be justified by different costs. b. The Robinson-Patman Act regulates spending levels and tax rates in the economy. c. The Robinson-Patman Act requires all reporting entities to organize their accounting and financial reports systematically. d. The Robinson-Patman Act regulates the accounting methods followed by firms in the United States