Eligibility for Employee plan participation in a qualified retirement plan may be postponed beyond one year of service if which of the following features is also part of the plan?

a. Contributions are 100% immediately vested upon eligibility

b. Contributions are made based on an age-weighted formula

c. Key employees must wait longer than rank-and-file employees to enroll

d. The employer agrees to match 100% of employee deferrals up to 10% of compensation