Which of the following vesting schedules may be used in a qualified plan (for employer contributions that are not matching contributions) that is not top-heavy?

I. 0-10 years of service, 0% vested; 11-14 years of service, 50% vested; 15 or more years of service, 100% vested

II. 0-3 years of service, 40% vested; 4 years of service, 80% vested; 6 or more years of service, 100% vested

III. 2 years of service, 20% vested; 3 years of service, 40% vested; 4 years of service, 60% vested; 5 years of service, 80% vested; 6 or more years of service, 100% vested.

A. I only

B. II only

C. III only

D. II or III

E. I, II, and III