Wilma has always used the services of a tax preparation firm to file her taxes...

Tax deductions are amounts that reduce your total income before calculating your tax payable. They lower your marginal tax rate, which is the tax rate that applies to your last dollar of income. For example, if Wilma’s total income is $50,000 and she claims $5,000 in tax deductions, her taxable income will be $45,000 and her marginal tax rate will be lower than if she had no deductions. Therefore, A is the correct answer. References: All deductions, credits, and expenses - Personal income tax - Canada.ca