17. Which of the following statements are true? a. Federal excise taxes are includable in gross receipts subject to tax. b. Import duties are subject to sales and use tax when the importer is the seller. c. The exemption for sales to the U.S. Government extends to sales of supplies and overhead allocated to various contracts. d. A sale to a contractor of a tool that he or she will use in the performance of a cost-plus-a-fee contraet to repair a Navy Ship is taxable. e. A sale of materials that the contractor will use to build an airplane under a qualifying fixed price contract with the United States Government is subject to tax