Paid vacations have undergone a steady liberalization as a worker benefit. As a result

a. 4-week vacations, usually after at least 15-years' service, are included in 90 percent of all agreements.
b. 95 percent of contracts, usually requiring 6–9 years' service, permit a 3-week paid vacation.
c. after 5 years of service almost all workers under contract receive a 2-week vacation.
d. All of the above.

D