need answer please...am stumped

3.Which of the following payments and benefits are subject to Canada Pension Plan contributions? Select one: a. Stephan received a $100 tip at the restaurant where he is head waiter and the restaurant determined the amount of the tip C b. Winona received a $100 gift certificate from her friends at work for her birthday c. Betty received a payment of $75 from her employer as a reimbursement for office supplies she had purchased from her own money C d. Harold took a one-year unpaid leave from his job to travel