Amy is a calendar year taxpayer reporting on the cash basis. Indicate which of the following income or expense items should not be included in her 2018 tax return. a. She pays all her outstanding invoices for standard business expenses in the last week of December 2018. b. On April 15, 2019, she makes a deductible contribution to an IRA for 2018. c. She sends out a big bill to a customer on January 1, 2019, even though she did all of the work in December of 2018. d. She prepays half a year of interest in advance on her mortgage on the last day of 2018.