For payroll withholding, income tax is calculated on taxable income for the pay period, so only deductions that are income-tax deductible (or otherwise reduce taxable income at source) will reduce the employee’s taxable base for withholding. Employee contributions to an RRSP are generally deductible for the employee, which is why payroll-deducted RRSP contributions (such as contributions to a group RRSP taken off the paycheque) reduce the amount of income tax withheld when the payroll system is set up to treat them as deductible contributions. The CRA confirms that deductible RRSP contributions can be used to reduce your tax.

By contrast, paying provincial health care premiums (where applicable) and paying an employee share of group benefit plan premiums are not automatic “reduce taxable income at source” deductions in the same way for payroll withholding; they may be personal expenses and, depending on the plan/premium type, may only affect the employee’s personal tax situation through credits/deductions when filing, not the standard payroll withholding base. Therefore, the only correct choice is A.