Which of the following benefits provided by an employer to its employees is taxable?

a.Employees of the XYZ Department Store are allowed a 5% discount on store merchandise. XYZs normal gross profit percentage is 20%.

b. Up to $3,000 of undergraduate tuition is waived by ABC University for university employees.

c. B.J. Airline provides free standby flights to its employees.

d. Rent-free use of corporate apartment