How does the amortization of tax-deductible goodwill affect the computation of a parent com- pany’s income taxes? a. It is a deductible expense only if the parent owns at least 80 percent of the subsidiary’s voting stock. b. It is deductible only as impairments are recognized. c. It is a deductible item over a 15-year period. d. It is deductible only if a consolidated tax return is filed.